Vehicle information system

ABSTRACT

A vehicle information system which includes an in-vehicle system  105  and a centralized server system  120.  The in-vehicle system communicates with the server system using a wireless communication link  110,  such as over a cellular telephone system. A position system, such as a set of GPS satellites  140,  provides positioning signals that are used by the in-vehicle systems, and optionally by the centralized server system to increase the accuracy of position estimates. In one version of the system, an operator specifies a destination to an in-vehicle system which validates the destination. The in-vehicle system transmits specification of the destination to a server system  125  at the centralized server. The server system computes a route to the destination and transmits the computed route to the in-vehicle system. The in-vehicle system guides the operator along the route. If the in-vehicle system detects that the vehicle has deviated from the planned route, it replans a new route to the destination using an in-vehicle map database.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.09/136,868, filed Aug. 19, 1998, which claims the benefit of U.S.Provisional Application No. 60/056,150, filed Aug. 19, 1997.

BACKGROUND

This invention relates to an information system for motor vehicles.

Vehicle information systems have been developed that provide varioustypes of information to operators of those vehicles. In particular,navigation systems have been developed. One type of navigation system,an autonomous navigation system, uses an on-board map, typically storedon a removable medium such as a compact optical disk (e.g., CD-ROM). Thenavigation system uses the on-board map to plan a route from a startingpoint to a destination, which is specified by the operator of thevehicle. Updating an autonomous system's map, for example to add orcorrect information, typically involves replacing the removable medium.

In some navigation systems the operator inputs the desired destination(and the current location, if required by the system) by entering aspelling of the destination. Some systems also allow an operator toselect from a stored list of “points of interest,” such as a list of gasstations or restaurants. Once the operator inputs the destination, thesystem plans a route along the road network to the destination. Theroute is typically planned to provide a shortest distance or to try toprovide the shortest travel time. Once the route is planned, theoperator is guided by the system along the route.

Various approaches to route guidance have been used. A particularlysimple approach is to provide the operator with a sequence of discreteinstructions, for instance, at intersections where the operator mustturn from one street onto another. The operator indicates when he or sheis ready for the next instruction. For example, the instructions areprovided as an audio output, and the operator says “next” when ready foranother instruction.

Another approach to route guidance uses a displayed map on which theplanned route and the vehicle's location are dynamically displayed. Theoperator uses the map to decide when and where to turn in order tofollow the planned route.

Some guidance approaches are aided by in-vehicle sensors that are usedto estimate the location of the vehicle. For instance, a magneticcompass is used to estimate the direction of travel, and a velocitysensor is used to estimate the distance traveled. In addition, thelocation of the vehicle can be estimated using the Global PositioningSystem (GPS). In GPS, multiple satellites emit signals that allow anin-vehicle GPS receiver to estimate its absolute location.

Other types of vehicle information systems have also been developed. Insome systems, traffic related information, such as traffic advisories,is broadcast to specially equipped in-vehicle radio receivers.

SUMMARY

In general, in one aspect, the invention is a vehicle informationsystem. The vehicle information system features an in-vehicle system anda centralized server system. The in-vehicle system communicates with theserver system using a wireless communication link.

In general, in another aspect, the invention is a method for guiding avehicle through a road network from a starting location to adestination. The method features transmitting a specification of thedestination to a server, for example by transmitting a street address oran identifier of a point of interest. The server determines a route tothe specified destination and transmits a specification of the route tothe vehicle. The method also includes receiving from the server aspecification of a planned route through the road network to thedestination as well as receiving from the server a map that includes aspecification of the road network in the vicinity of the planned route.For instance, the map can correspond to one or more regions aroundparticular points on the planned route, correspond to a “corridor”around the planned route, or be a complex shaped region in the vicinityof the route. The planned route can include specifications of a multiplemaneuvers to be carried out by the vehicle, and the specification ofeach maneuver then includes a location of the maneuver. The map can bein the vicinity of the starting location, or in the vicinity of one ofthe specified maneuvers. The method can also feature tracking thelocation of the vehicle. The method can also feature displaying thereceived map in conjunction with a representation of the planned route,and a location of the vehicle.

An advantage of the invention is that the vehicle does not have to havea prestored map to plan a route to a destination. Also, the inventionprovides a way of displaying a map of the vicinity of the starting pointor of intermediate maneuver points of a planned route without requiringthat the map be prestored in the vehicle. The displayed map can provideuseful information to an operator of a vehicle during difficultmaneuvers where turn-by-turn instructions.

In general, in another aspect, the invention is a method for tracking avehicle. The method features receiving a reference signal from apositioning system, for example receiving signals from GPS satellites,and computing position data related to the location of the vehicle usingthe received reference signal. For example, the position data can belatitude and longitude estimates, or can be GPS pseudorangemeasurements. The method also features transmitting the position data toa server and receiving from the server position correction data. Forexample, the position correction can be a deviation in latitude andlongitude, or can be correction terms to be applied to GPS pseudorangemeasurements. The method also features determining estimated coordinatesof the vehicle including combining data computed from the receivedreference signal and the position correction data.

The method can feature repeatedly computing the position data, anddetermining the estimated coordinates, including combining the positiondata and the position correction data. The method can also feature,subsequent to the interval of time, repeatedly computing the positiondata and determining estimated coordinates of the vehicle using theposition data without using the correction data.

In general, in another aspect, the invention is a method for tracking avehicle. The method features receiving a specification of a firstlocation which includes coordinates, such as latitude and longitude, ofthe first location. The method includes determining when the vehicle isat or passes near the first location. The method includes computingfirst position data using a reference signal received from a positioningsystem at the time at which the vehicle was determined to be at thefirst location. For instance, the positioning system can be a GPSpositioning system, and the computed first position data can includepseudorange measurements derived from GPS satellite signals receivedwhen the vehicle was at or near the first location. The method furtherincludes computing position correction data using the first positiondata and the coordinates of the first location. For instance, computingthe position correction data can include computing pseudorangecorrection data based on the latitude and longitude of the firstlocation and on the pseudorange measurements derived from GPS satellitesignals received when the vehicle was at or near the first location. Themethod further includes computing second position data using a referencesignal received from the positioning system at a second time subsequentto the time at which that the vehicle was determined to be at the firstlocation, and then determining coordinates of the vehicle at the secondtime including combining the correction data and the second positiondata.

The method can feature including in the specification of the firstlocation a specification of a maneuver to be carried out by the vehicleat the first location. Determining when the vehicle is at the firstlocation then includes detecting when the vehicle performs the specifiedmaneuver, for instance using vehicle sensors such as a compass,accelerometers, or a gyroscope.

In general, in another aspect, the invention is a method for detectingwhen a vehicle deviates from a planned route. The method featurestracking a first estimated position of the vehicle using signals from apositioning system that are received at the vehicle, for example, usinga GPS positioning system. The method also features tracking a secondestimated position of the vehicle using an estimate of the distancetraveled along the planned route. The vehicle is detected to hasdeviated from the planned route when the first estimated position andthe second estimated position differ by at least a tolerance distance.

The method can feature detecting when the vehicle is at a first point onthe planned route, such as a maneuver point, and estimating the distancetraveled along the path following the first point.

The method can also feature adjusting the tolerance distance, includingreducing the tolerance distance when the vehicle is detected to be atthe first point on the planned route, and increasing the tolerancedistance as the vehicle travels along the path following the firstpoint.

In general, in another aspect, the invention is a method for providingguidance instructions to a vehicle operator following a planned routethat includes a sequence of maneuver points. The method includesdetecting when the vehicle is at a first maneuver point, and trackingthe distance traveled by the vehicle from the first maneuver point alongthe planned route. When the tracked distance is within a predeterminednotification distance of the distance between the first maneuver pointand a subsequent maneuver point along the planned route the operator isnotified of the subsequent maneuver.

In general, in another aspect, the invention is a method for specifyinga location in a vehicle navigation system. The method features providingan in-vehicle map database to an in-vehicle system. The in-vehicledatabase includes data related to valid location specifications foraccessing a server map database at a server system. The method alsofeatures accepting a location specification, for instance, for anoperator using a user interface in the vehicle. The system validates thelocation specification using the in-vehicle map database and thentransmits the validated location specification to the server system.

The method can also feature providing the server map database to theserver system and accessing the server map database using the receivedvalidated location specification. In addition the method can alsoinclude determining a route to the specified location using the servermap database, and transmitting the determined route to the in-vehiclesystem.

In general, in another aspect, the invention is method for estimating alocation of a vehicle. The method includes determining a series ofvehicle position estimates using a positioning system, and recordingeach of the vehicle position estimates in the series. For example, theposition estimates are recorded in a non-volatile memory as the vehiclereaches a destination. The method further includes estimating thelocation of the vehicle including retrieving the most recently recordedin the series of location estimates, for instance after the vehicle isstarted after a period of being parked at the destination.

The invention has the advantage that a location estimate may beobtained, even if a positioning system, such as a GPS satellite system,is out of range, or prior to the positioning system being initialized.

In general, in another aspect, the invention is a method for vehicleguidance. The method features receiving at the vehicle a planned routeto a destination location from a server, and storing the planned routeat the vehicle. The method also includes providing instructions to anoperator of the vehicle according to the stored planned route, forexample, providing instructions at each of a series of maneuvers alongthe route. The method includes tracking a location of the vehicle anddetecting whether the vehicle has deviated from the planned route. Ifthe vehicle is detected to have deviated from the planned route, themethod then includes planning a new route to the destination location.Planning the new route does not necessarily require furthercommunication with the server. Planning the new route can includedetermining the location of the vehicle and accessing a map databasestored in the vehicle.

The method can also include establishing a wireless communicationchannel with the server, transmitting a specification of the destinationlocation over the wireless communication channel, and then terminatingthe wireless communication channel after receiving the planned route.

Advantages of this method include providing a server based routeplanning service to a vehicle, without requiring ongoing communicationwith the server to carry out guidance and route replanning functions.

In general, in another aspect, the invention is a method for collectingtraffic information. The method includes tracking the location of avehicle, including detecting when the vehicle traverses each of aplurality of segments of a road network. For each detected segment, themethod includes logging traffic-related data, including logging datarelated to the vehicle's speed on the detected segment. The method thenincludes transmitting the logged data to a server

The method can feature receiving a command from the server to enablelogging of the traffic-related data at a vehicle. The method can alsofeature receiving at a vehicle a request to transmit the logged data tothe server.

In general, in another aspect, the invention is a method for collectingtraffic information. The method includes tracking the location of avehicle, including detecting when the vehicle traverses each of a set ofsegments of a road network. For each detected segment, the methodfeatures comparing the vehicle's speed on the segment to a stored speedfor that segment, and if the vehicle's speed on the segment deviatesfrom the stored speed, transmitting a traffic notification identifyingthat segment to a server.

In general, in another aspect, the invention is a method for collectingtraffic information. The method includes receiving traffic related datafrom a set of vehicles and updating a traffic database using thereceived traffic related data. Updating the database includes updatingspeed information associated with multiple road segments in a roadnetwork. The method also features planning a route through the roadnetwork from a starting to a destination location using the speedinformation associated with the road segments.

The method can also feature enabling a subset of an available set ofprobe vehicles to provide the traffic related data, and can, inaddition, feature determining a part of the traffic database to targetfor updating, for instance, according to a the part of the databasecorresponding to a geographic area. Enabling the subset of probevehicles then includes enabling probe vehicles according to the part ofthe database that is targeted.

In general, in another aspect, the invention is a method for specifyinga destination to a vehicle navigation system. The method includesaccessing a list of categories of destinations, and accepting aselection from the list of categories, for example, from an operatormaking the selection on a in-vehicle user interface. The method includestransmitting the selection from the list of categories to a serversystem, and subsequently receiving a list of destinations from theselected category from the server system. The method then includesaccepting a selection from the list of destinations and transmitting theselected destination to the server system.

The method can also feature transmitting data related to the location ofthe vehicle to the server system. The received list of destinations thenincludes destinations that are in the vicinity of the vehicle.

In general, in another aspect, the invention is a method for configuringa vehicle navigation system. The method includes providing a server mapdatabase to a server. The server map database includes data related to aplurality of road segments in a road network. The method also includesproviding a vehicle map database to an in-vehicle system. The vehiclemap database includes data related to a subset of the plurality of roadsegments in the server map database which satisfy a common criterion,for instance related to the road class of the road segments.

In general, in another aspect, the invention is an in-vehicle mapdatabase. The database includes a first stored table and a second storedtable. The first stored table includes multiple records each including afield containing a reference to a record containing a base name of astreet in the second stored table, and a second field which identifies aprefix, a suffix, or a street type. The second stored table includesmultiple records, each including a base name of a street stored in acompressed format.

In general, in another aspect, the invention is method for transmittinga route to a vehicle navigation system. The route includes multipleintermediate points joined by road segments. The method includestransmitting a specification of the location of a first of theintermediate points, and transmitting a specification of a differencebetween the location of a second of the intermediate points and thefirst of the intermediate points. The specification of the differencecan use fewer than an allocated number of bits.

The method can also feature planning an initial route. The initial routeincludes an initial set of multiple intermediate points coupled by roadsegments. The planned route is formed from the initial route. For any ofthe road segments in the initial route for which the difference inlocations of the intermediate points bounding that segment is greaterthan can be specified in the allocated number of bits, the methodincludes inserting additional intermediate points on that road segmentso that the differences between the locations of the adjacentintermediate points can each be specified in the allocated number ofbits.

In general, in another aspect, the invention is a vehicle navigationsystem. The system includes an onboard computer, including storage for amap database, a wireless communication system for passing data betweenthe onboard computer and a remote server, an input/output device forproviding a user interface between the onboard computer and an operatorof the vehicle, and a vehicle sensor for providing motion-relatedsignals to the onboard computer. The onboard computer is programmed toperform the functions of accepting a planned route from the server overthe wireless communication system, maintaining a first location estimateof the vehicle using the motion-related signals from the vehicle sensor,and, using the planned route and the first location estimate, providingguidance instructions to the operator through the input/output device.

In general, in another aspect, the invention is a method for updating anin-vehicle navigation system. The method includes receiving a versionnumber associated with information stored in the in-vehicle system. Ifthe information stored in the in-vehicle system has a version numberprior to the version of information a server, the method includestransmitting update information from the server to the in-vehiclesystem. The information stored in the in-vehicle system can include mapdata or computer instructions.

The method can feature prioritizing the update information, forinstance, according to the geographic area represented by the updateinformation and transmitting the update information in order of thepriority.

In general, in another aspect, the invention is a vehicle informationserver system. The system includes a vehicle communication interface forproviding wireless data communication between multiple vehicles and aset of information system. The set of information systems includes anavigation system for accepting route planning request from the vehiclesand providing planned routes through the communication interface, and acommunication system coupled to an external information system fordelivering information from the external information system to thevehicles.

In general, in another aspect, the invention is a method for providingtraffic related information to a user. The method features acceptingfrom the user a specification of a path made up of one or more roadsegments in a road network and receiving traffic data related to roadsegments in the road network. If the received traffic data indicates anexceptional traffic condition on the specified path, the user isnotified of the traffic condition.

Other features and advantages of the invention will be apparent from thefollowing description, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a vehicle navigation system;

FIG. 2 is a block diagram of in-vehicle components of the system;

FIGS. 2A-C show an integrated input/output device;

FIG. 3 is a block diagram including components of a server system;

FIGS. 4A-B show an in-vehicle system software architecture;

FIG. 5 is a block diagram of a server system software architecture;

FIG. 6 is a schematic map showing the road network in an exemplaryregion;

FIG. 7 is a graph representation of the road network in the exemplaryregion;

FIG. 8 illustrates an exemplary planned route that is downloaded from aserver system to a vehicle;

FIG. 9 is an exemplary spot map that is downloaded from a server systemto a vehicle;

FIG. 10 is a main roads map that is preloaded in a vehicle;

FIG. 11 shows data structures of an in-vehicle database;

FIG. 12 shows the structure of text tables in the in-vehicle database;

FIG. 13A shows a representative link of a main roads network;

FIG. 13B shows data structures of an in-vehicle database encoding a mainroads network;

FIG. 14 shows elements of an in-vehicle database which encode Points ofInterest information;

FIG. 15A is a pseudocode listing of an in-vehicle route planningprocedure;

FIG. 15B is a pseudocode listing of a server route planning procedure;

FIG. 16 is a pseudocode listing of a startup maneuver procedure;

FIG. 17 is a pseudocode listing of a route following procedure;

FIG. 18 is a pseudocode listing of a route replanning procedure;

FIG. 19 illustrates a extensible server architecture;

FIGS. 20A-20C illustrate approaches to updating an in-vehicle system;

FIGS. 21A-21B illustrate additional information services provided by aserver system; and

FIG. 22 is a block diagram of an extensible server system.

DESCRIPTION

1 Overview (FIGS. 1, 6-10)

1.1 Architecture (FIG. 1)

Referring to FIG. 1, a vehicle information system provides services,including a route planning and guidance (i.e., a “navigation”) service,to the operators of multiple vehicles 100, which are free to drivethroughout a wide geographic area. To provide these services to theoperators of the vehicles, the vehicle information system performs somefunctions in a server system 125 at a centralized server 120 that is ata fixed location, and other functions in in-vehicle systems 105installed in each of the vehicles 100. The vehicle information systemalso includes a positioning system that provides a reference forestimating the locations of vehicles 100 in absolute terms (i.e., interms of their latitudes and longitudes). In particular, GlobalPositioning System (GPS) satellites 140 provide signals that whenreceived at the vehicles enable the in-vehicle systems to estimate theirlocations.

The navigation service of the vehicle information system as a whole,which are provided through a combination of functions that are performedby server system 125 and by an in-vehicle system 105, enable an operatorof a vehicle to specify a desired destination, and then to be guided bythe system to that destination while driving the vehicle. In-vehiclesystem 105 tracks (i.e., repeatedly estimates) the position of thevehicle as it travels to the desired destination, and providesinstructions to the operator to guide the operator to the desireddestination. For instance, in-vehicle system 105 provides an instructionto make a turn at an upcoming intersection while the vehicle isapproaching the intersection. Also, in-vehicle system 105 typicallydetermines when the operator has made an error and the vehicle is off aplanned route. If the vehicle is off route, in-vehicle system 105provides the operator with instructions to continue to guide the vehicleto the destination despite the error.

Server system 125 provides various services to in-vehicle system 105, ina “client-server” arrangement in which in-vehicle systems 105 requestservices from server system 125. For instance, a route planning functionis performed by server system 125 at the request of in-vehicle system105 while route guidance functions are performed by in-vehicle system105.

In-vehicle systems 105 are coupled to server system 125 by wirelesscommunication links. In particular, in-vehicle systems 105 at timescommunicate with server system 125 over signal paths 110 using modulateddata signals that are passed over a standard analog cellular telephonesystem (i.e., using the Advanced Mobile Phone Service (AMPS) standard).An in-vehicle system 105 typically operates in an autonomous mode afteran initial exchange with server system 125. During the initial exchange,a starting location (or other location-related data), speed and heading,and a desired destination are uploaded from the in-vehicle system to theserver system and then a planned route is downloaded from the serversystem to the in-vehicle system. After planned route information isdownloaded to the vehicle from the server system, the in-vehicle systemdoes not require further interaction with the server system to operatein its autonomous route guidance mode. While in the autonomous routeguidance mode the in-vehicle system can recover from an operator goingoff the planned route without necessarily requiring furthercommunication with the server system.

In-vehicle systems 105 receive signals from GPS satellites 140 overradio frequency communication paths 112. Server system 125 also receivessignals from GPS satellites 140 over radio frequency communication path122. As is described more fully below (see Section 2.4), data derivedfrom signals received by server system 125 from GPS satellites 140 isused at times by both server system 125 and in-vehicle systems 105 toimprove the location estimates of vehicles 100, for instance, using“differential” GPS calculations.

Referring still to FIG. 1, server system 125 relies on a map provider160, for instance, a vendor of map-related information, to provideinformation related to the road network, including the locations andtypes of road segments that interconnect to form the road network. Mapprovider 160, or some other external information provider, also providesother map-related information such as the locations of typical points ofinterest such as city centers, restaurants, and gas stations.

In some versions of the system, server system 125 also serves as agateway to external information systems 130. These external systemsprovide information used by server system 125, or provide informationthat is passed directly to in-vehicle systems 105. For instance, anexternal information system 130 can provide traffic-related informationthat is used by server system 125 to determine a fastest route from astarting to a destination location. In another instance, an externalinformation system 130 can provide communication services to vehicleoperators, such as a paging service.

Alternative communication approaches between in-vehicle systems 105 andserver system 125 can be used. Use of standard analog cellular telephonelinks is useful due to the broad geographic coverage in North America ofthe infrastructure needed to support such links. In other parts of theworld, digital cellular telephone links may be more appropriate if thenecessary infrastructure is available. Such a digital-basedinfrastructure is expected to be available in North America in thefuture. A satellite-based communication system can alternatively be usedto link the in-vehicle systems to the server system. Also, otherwireless data communication systems can be equivalently used to couplein-vehicle systems 105 and server system 125. Such systems are currentlybeing deployed in North America (e.g., ARDIS, RAM, CDPD, GSM), althoughthe geographic coverage is not yet adequate to support this system andprovide broad geographic availability to vehicle operators. Manywireless communication systems also include a “short message” capabilitywith which short messages can be transferred. Such short messageservices can alternatively be used for some types of communicationbetween the in-vehicle systems and the server system, for instance fornotification of exception conditions.

Also, alternative positioning systems can be used rather than relying onsignals from GPS satellites 140. For instance, a roadside optical orradio frequency beacon systems can be used to provide locationinformation to vehicles. Such a roadside beacon system is not broadlyavailable in North America. On the other hand, the GPS-based approachprovides broad geographic coverage today.

Centralized server 120 is “centralized” in that it provides services atone location for vehicles that are distributed throughout a geographicarea. The centralized server's location does not have to be “central” oreven located in the same geographic area as the vehicles it services.Also, although the system is described in terms of a single centralizedserver 120, multiple servers can alternatively be used. When multipleservers are used, in-vehicle systems 105 can be configured to accessparticular servers for all, or for particular types of, servicerequests.

1.2 Operation (FIGS. 6-10)

General operation of the navigation service of the vehicle informationsystem can be understood with reference to FIGS. 6-10, which illustratevarious representations of exemplary maps and routes that are used inthe system. These drawings correspond to a common geographic area thatis shown schematically in FIG. 6. The geographic area shown is only avery small portion of the area that is typically supported by thenavigation service, which may be as large as the United States ormultiple countries in Europe.

Referring to FIG. 6, a map 600 is illustrated with three classes ofroads shown in different line widths. In general, roads are classifiedaccording to their size or typical vehicle speed, for example, highways,limited access roads, main roads, and side streets. In FIG. 6, a highway610 is shown as a thick line running along the vertical orientation ofthe drawing. A set of main roads 620, 622, 624, and 626, which is shownin medium thickness lines, form an intersecting network. Main roads 620and 622 are connected to highway 610 at two on-ramps, 612 and 614,respectively. A set of residential roads (side streets) 630-636completes the road network.

In this example, an operator and vehicle are initially at the pointmarked ‘X’ 690. The operator wants to get to a desired destination 692that is not shown in the drawings, but that is best accessed byfollowing highway 610 as indicated in the drawings.

As the first step, the operator enters a specification of desireddestination 692 into in-vehicle system 105. For instance, the operatorenters the city, street, and street number of a destination address. Thedestination is validated by the in-vehicle system, for instancevalidating that the street address is in an allowable range for thespecified street.

After in-vehicle system 105 has accepted and validated the destinationspecification, it establishes a communication session with server system125 over cellular telephone link 110 and sends the destinationspecification to the server system. The in-vehicle system also sendsinformation to the server system that allows the server system todetermine the vehicle's starting location 690. For instance, thein-vehicle system sends the estimated latitude and longitude outputobtained from a GPS receiver in the vehicle, or sends other raw outputfrom its GPS receiver.

Referring to FIG. 7, the server system includes a stored detailedrepresentation of the road network 700. The network is represented as agraph with a set of nodes, indicated in the drawing by open circles,that are interconnected by links (arcs) that correspond to roadsegments. Links in the graph have associated stored data which includesthe class of the road represented by the links. Each node in the graphhas associated data including its latitude and longitude (orequivalently its relative location to another node that is at a knownlocation), as well as other information, such as which turns from onelink to another link joined at the node are valid. Many links areapproximated by straight line segments joining the nodes at each end ofthe link. Some links, such as the links joining nodes 733 and 735 ornodes 716 and 725, represent curved road segments. To represent suchcurved road segments, links can include one or more “shape points,”represented as hatched circles 780-785 in the drawing. Each shape pointhas location data associated with it. The segments between adjacentshape points, or between nodes and adjacent shape points, areapproximated by straight line segments.

Server system 125 uses the information provided by the in-vehicle systemrelated to the location of the vehicle 690 to determine the startinglatitude and longitude of the vehicle. Based on the vehicle's latitudeand longitude, speed, and heading, the server system finds the vehicle'sstarting link in its graph representation of road network 700. In thisexample, this first point on the road network is on the link joiningnodes 753 and 763.

The server system next computes a best path to destination 692. “Best”can be based on a variety of criteria such as the smallest totaldistance, or the shortest expected travel time using information relatedto the expected speed of travel along links of the roadway graph. Inthis example, this planned route is illustrated by the dotted line 792.Referring back to FIG. 6, this planned route has the vehicle starting onresidential road 635 and first making a left on residential road 632.The vehicle then is to make a right turn onto main road 628, and a rightonto main road 620. Main road 620 merges onto highway 610. The vehiclethen is to continue along highway 610 toward destination 692.

Referring to FIG. 8, planned route 800 is downloaded from the serversystem to the in-vehicle system in the form of a sequence of linksjoined by nodes. Each node along the route (other than necessarily thestart node) corresponds to a node in the server's road network 700 (FIG.7). Nodes along planned route 800 correspond to “maneuvers” that must becarried out by the operator. For example, the maneuver at node 790 is“turn left onto road 635” (See FIG. 6). Each link along the route canhave one or more “way points.” Way points correspond to shape points inthe server's road network 700, or to nodes which are intersections atwhich the operator does not have to make a maneuver, that is, nodes ofthe server's road network 700 at which the operator simply continueswithout turning or making some other maneuver. In FIG. 8, nodes 733,780, and 781 are way points on the link joining maneuver points 732 and735.

In principle, if the operator could always be expected to followdirections exactly, then the operator will drive to the desireddestination. However, various factors may result in the operator notreaching the desired destination without further planning. These factorsinclude:

Inaccuracy in the estimate of the vehicle's initial location, forexample due to closely spaced side streets,

The operator's inability to follow directions, particularly during theinitial startup portion of a route where the directions may becomplicated,

Errors in the system's map of the road network, for instance, due tounexpected road construction, and

Inaccuracy in estimating the distance traveled by the vehicle.

In order to account for errors associated with the startup portion ofthe route, the server system downloads to the in-vehicle system adetailed map 900, known as a “spot map,” around initial location 690.Referring to FIG. 9, map information related to nodes and links in thevicinity of starting location 690 are downloaded. Spot map 900 has ashigh a level of detail as does the server's road network 700, but islimited geographically, for instance including all nodes within twolinks of the starting location.

The server system can also download a spot map around one, or more,maneuver points, or around the destination. For instance, if a maneuveris particularly complex, the server system would download a spot maparound that maneuver point.

After planned route 800 and spot map 900 are downloaded to the vehicle,communication between in-vehicle system 105 and server system 125 istypically completed. At this point, the operator can preview the route,or can start traveling to the destination. The operator can also starttraveling before the planned route is downloaded. The in-vehicle systembegins providing initial guidance commands and displaying the spot maparound the starting location to the operator as soon as it is downloadedwithout necessarily waiting for the complete route to be downloaded.

While traveling to the destination, the in-vehicle system attempts totrack the location of the vehicle. As the in-vehicle system determinesthat the vehicle is approaching each maneuver point, it provides auraland graphical instructions to the operator regarding the action to takeat that maneuver point. If a spot map has been downloaded for themaneuver, the in-vehicle system displays the spot map in addition to, orinstead of, the graphical instructions.

During the initial portion of the trip or near a maneuver for which theserver system has provided a spot map, while the vehicle is in theregion of a spot map 900, the spot map is used by the in-vehicle systemto guide the operator onto the planned route. In particular, thein-vehicle system displays the spot map and the initial portion of theplanned route to the operator. In addition, the in-vehicle systemdisplays the tracked location of the vehicle in conjunction with thespot map. This allows the operator to recover from errors during theinitial portion of the trip by seeing that the tracked location is notfollowing the planned route, and using the roads shown on the spot mapto determine what turns to make to get back to the planned route.

The in-vehicle system also has a preloaded main roads network 1000,which is a stored version of the map that includes only main and largerroadways (i.e., it does not include residential roads). A portion of themain roads network 1000 is shown in FIG. 10. Main roads network 1000 hasa similar form as the server's road network 700 shown in FIG. 7, exceptthat fewer links are included. For reference, the planned route 792 isillustrated by a dotted line.

While traveling toward the destination, the in-vehicle system tracks anestimated location of the vehicle. If the operator does not properlyfollow the directions, the in-vehicle system will typically detect whenthe vehicle has diverged too far from the planned route. When it detectsthat the vehicle is off-route, it plans a corrected route based on themain roads map shown in FIG. 10 which get the vehicle back onto theoriginally planned route

Referring back to FIG. 6, in this example, the operator fails to makethe right turn from main road 628 onto main road 620, continuing insteadon main road 628. Referring back to FIG. 10, the in-vehicle systemdetermines that the vehicle is off-route at a point 1010, whichcorresponds to a point on a main road segment between nodes 732 and 722when it should have been at a point on the link joining points 732 and735. Using its main road network 1000, the in-vehicle system plans acorrected route indicated by the dashed line 1012. This re-planned routejoins the originally planned route at point 725. Note that in replanninga route after an off-route condition occurs, the in-vehicle system doesnot necessarily have to contact the server system, relying instead onits main roads network 1000.

The in-vehicle system therefore uses a combination of main roads network1000 that is preloaded into the vehicle and spot maps 900 that aredownloaded to the vehicle along with planned route 800 to replan theroute when the vehicle is detected to not be following the plannedroute.

In an alternative version of the system, spot maps 900 can be used toaugment main roads network 1000 to re-plan the route if the operatorfails to follow the planned route during the initial portion of thetrip.

In the system operation described above, a vehicle operator receivesinstructions in the form of

Graphically presented maneuver instructions,

Aural maneuver instructions, and

Spot map based instructions.

Alternative versions of the system use subsets of these forms ofinstructions. For instance, a version of the system can use auralinstructions alone. Another version of the system can use graphicallypresented maneuver instructions without any map based or auralinstructions. Other combinations or instruction modes can be used aswell. Furthermore, alternative versions of the system can give thevehicle operator control over which instruction modes are used, forinstance, allowing the operator to switch between map based andgraphical instruction based modes.

2 Hardware and Software Architecture (FIGS. 2-5)

2.1 In-vehicle System Components (FIG. 2)

Referring to FIG. 2, each in-vehicle system 105 includes an onboardcomputer 210 which is used to coordinate the operation of othercomponents, including sensors 230, which provide information related tothe motion of the vehicle, input/output (I/O) devices 240, which providean interface between the operator of the vehicle and the navigationsystem, and communication system 250, which provides communication linksfrom GPS satellites 140 and to and from server system 125. Onboardcomputer 210 is also coupled to vehicle systems 270, which include doorlocking system 272 and airbag system 274.

Onboard computer 210 has limited storage and processing capabilities. Inthis version of the in-vehicle system, onboard computer 210 includes aprocessor 212 coupled to other components of the onboard computer over adata bus 214. The other components includes dynamic random access memory(DRAM) 220, which provides 2 MB of working storage for processor 212,erasable programmable read-only memory (EPROM) 218, which provides 4 MBof non-volatile storage, and universal asynchronous receiver-transmitter(UART) 216, which provides serial communication capabilities to othersystem components. Alternative hardware configurations, for instance,with more or less memory, can be used.

Processor 212 is also coupled to a static storage 222 which is anon-volatile storage used to store code and data for operation of thesystem. In particular, as is described further below, static storage 222is used to store map-related information, such as main roads network1000 (FIG. 10), which is used during route planning and guidanceprocedures executed on onboard computer 210. Static storage 222 is aremovable 40 MB flash memory system which emulates a disk storagedevice. Alternative static storage devices can be used, includingremovable and non-removable disk storage devices and semiconductormemories.

Sensors 230 include a velocity sensor 232 which provides a velocitysignal to onboard computer 210. The velocity signal encodes the distancetraveled by the vehicle by providing a constant number of pulses perrevolution of the output of the vehicle's transmission, and whichtherefore provides a relative constant number of pulses per miletraveled. Sensors 230 also includes a magnetic compass 234 whichprovides a signal to onboard computer 210 encoding the orientation ofthe vehicle. Alternative versions of the system do not necessarilyinclude magnetic compass 234, relying only on the velocity signal. Also,alternative versions may include other sensors of the state of thevehicle, including a gyroscope or accelerometers for determining therate of rotation of the vehicle, or a differential velocity sensor,which provides the relative speed of the wheels on either side of thevehicle thereby encoding a turning radius of the vehicle as it goesthrough a turn.

I/O devices 240 includes a display 242. In versions of the in-vehiclesystem in which only graphical commands are displayed, display 242 is asmall (e.g., 4-5 lines of text high, 64×240 pixels) monochrome liquidcrystal display (LCD) which is used to provide text and schematic imageinstructions to the operator of the vehicle. In versions of thein-vehicle system in which spot maps are displayed to the operator,display 242 is 4 to 5 inch diagonal display with approximately 200×200pixels, which is large enough and has a high enough resolution toprovide a detailed map display to the operator that can be used toprovide map-based directions to the operator. Also, in alternativeversions of the system, visual feedback is not necessarily used, relyinginstead solely on audio instructions from the system to the operator.

I/O devices 240 also includes an input device 244. Input device 244includes multiple push buttons associated with display 242. The operatoruses these buttons to select alternatives shown on display 242, or toscroll the list of displayed alternatives. Alternative versions of thesystem can include an alphanumeric keyboard coupled to the onboardcomputer.

Referring to FIGS. 2A-C, an integrated I/O device 241 includes display242 and a set of four rocker switches that are part of input device 244.One rocker switch is dedicated to “menu” and “cancel” inputs while theother three are reconfigurable. Referring to FIG. 2A, display 242 is attimes used to display both text commands and graphical representationsof commands. Referring to FIGS. 2B-C, display 242 is used at times toprovide visual feedback to the operator when inputting information. FIG.2B illustrates selection from a list and FIG. 2C illustrates spelledinput in which the operator uses the rotary switch to select letters tospell an input word.

Referring back to FIG. 2, I/O devices 240 also include a voice outputdevice 246. Voice output device 246 provides audio output of speechcommands that are stored or formed on onboard computer, for example,using compressed or concatenated waveforms or a speech synthesizer.

I/O devices 240 can be dedicated to onboard computer 210, or canalternatively be part of another vehicle component such as a radio. Inthe latter case, display 242 and input device 244 are the display andinput buttons of the other component, respectively. Many audiocomponents include standard control interfaces, such as the ACP (AudioControl Protocol) interface used in vehicles manufactured by the FordMotor Company. In such a case, onboard computer 210 can communicate withthe audio component using a standard communication interface. Voiceoutput can be provided to the operator by passing it through the audiosystem, or alternatively, onboard computer 210 can mute or attenuate theaudio system while voice output is provided through a dedicated audiopath.

Referring still to FIG. 2, communication system 250 includes a GPSreceiver 252 coupled to a GPS antenna 253 for receiving signals from GPSsatellites 140. GPS receiver 252 repeatedly provides location-relatedinformation to onboard computer 210, for example, at one-secondintervals. The location related information can be an estimatedlocation, in terms of latitude and longitude, or other raw measurementsthat can be used to compute an estimated location. GPS receiver 252 canalso receive correction data from onboard computer 210, which it uses tocompute increased accuracy location estimates from its raw measurements.As is described further below, the correction data can be provided byserver system 125 and is used at times to increase the accuracy of thelocation information provided by GPS receiver 252.

Communication system 250 also includes a cellular transceiver 254coupled to a cellular telephone antenna 255. Cellular transceiver 254provides voice and data communication capabilities to the vehicle. Amodem 256 is coupled between onboard computer 210 and cellulartransceiver 254. Data sent to and received from server system 125 over acellular telephone line passes through modem 256. Cellular transceiver254 is also coupled to a handset 260. The operator can place standardtelephone calls using handset 260 when cellular transceiver 254 is notbeing used to communicate with server system 125.

2.2 Server System Components (FIG. 3)

Referring to FIG. 3, server system 125 includes a server computer 310,which communicates with in-vehicle systems 105. Server system 125includes a telephone interface 320 for receiving and placing telephonecalls to establish data communication sessions with individualin-vehicle systems 105.

An in-vehicle system 105 initiates a communication session with serversystem 125 by placing a cellular telephone call to a telephone numberassociated with the server system. The call is routed through a cellulartelephone network 350 to public switched telephone network (PSTN) 340and then to telephone interface 320. Telephone interface 320 answers thecall. Telephone interface includes a modem function which is used toestablish a data connection with modem 256 (FIG. 2) in the callingvehicle. In alternative versions of the system, telephone interface 320may be coupled directly to cellular telephone network 350. Also, thedata signal may be demodulated prior to reaching the server system, forexample, in the telephone network itself.

The server system can similarly establish a data communication sessionwith a particular vehicle by placing a telephone call to the telephonenumber associated with that vehicle. Cellular transceiver 254 (FIG. 2)determines whether the inbound call is a data call from the serversystem or a voice call intended for voice communication with theoperator of the vehicle. A data call is connected to modem 256 (FIG. 2)providing a data connection between telephone interface 320 and modem256.

Server system 125 also includes a GPS receiver 325. GPS receiver 325receives signals from GPS satellites 140. Server system 125, which is atthe known location of centralized server 120, does not rely on GPSreceiver 325 to determine its location. Rather, server computer 310provides its known location (i.e., latitude and longitude) to GPSreceiver 325. Using the satellite signals and the known location of theserver, GPS receiver 325 provides in return GPS correction data, forinstance, “differential” pseudorange correction data provided accordingto the Radio Technical Commission for Maritime Services (RTCM) standardRTCM SC-104. This correction data is used to improve the locationsestimates of vehicles 100, as is described more fully in Section 2.4.

Server computer 310 includes a processor 312, working memory 314, andstatic storage 316. Static memory 316 includes storage for map-relatedinformation that is used by the server system in computing routes.

Server computer is coupled to external information systems 130. Forinstance, external information systems can be other computers coupled toserver system 125 over a data network 330, such as the Internet.

Server system 125 receives map information from map provider 160 on aremovable computer medium 360, such as a optical disk (e.g., CD-ROM).Server computer 310 reads this map data and stores a processed form ofthe map information in static memory 316 for further use. Alternatively,map provider 160 can provide the map information to the server system insome other way, for example by passing it to the server system over datanetwork 330.

2.3 Map Database

The in-vehicle and server systems make use of data derived from mapinformation furnished by map provider 160 on computer medium 360 (FIG.3). The raw map information furnished by map provider 160 includesvarious types of information related to the road network for aparticular geographic region, such as a portion of the United States.Within this region, the information includes a representation of theroad network as a graph as illustrated in FIG. 7. Links in the graphcorrespond to segments of the road network, for example, a segment of astreet between two intersections. Nodes in the graph correspond tointersections or other points at which two or more links join. Nodesthat couple only two links are used, for example, as “shape points” whena single roadway makes a turn. This allows roadway to be wellapproximated by sequences of straight segments.

The map information includes the locations of nodes in the graph, interms equivalent to their latitude and longitude. The map informationalso includes link information, including associations of street namesand links, and ranges of street numbers on links. Links are alsocategorized according to their size ranging from small residentialstreets to interstate highways.

An example of a map provider for this system is NavigationalTechnologies Inc. (NavTech) of Rosemont, Ill. The map information isprovided in one of a number of interchange formats, such as in theGeographic Data File (GDF) format, an international standard format. Amap in GDF format includes a data structure which associates links andnodes and their attributes, and relationships between nodes and links inthe graph. NavTech provides maps in which road links are categorized byclasses from 0 to 4, with 0 for residential (side) streets, 1 for mainstreets, 2 for arterial roads, 3 for freeways, and 4 for interstatehighways.

In alternative versions of the system, other forms of map informationthat can be converted to a link and node representation of a roadnetwork can alternatively be used.

2.4 GPS and DGPS Correction

As outlined above, both the in-vehicle and server systems include GPSreceivers. GPS positioning uses the ranges to multiple satellites thatare in precisely known orbits around the earth. A constellation ofapproximately 24 satellites is in such known earth orbits. A receiver atany point on or near the surface of the earth is typically in range of asubset of three or more of the satellites. A GPS receiver determines anestimate of its distance or range (a pseudorange measurement) to each ofthe subset of in-range satellites. It then computes itsthree-dimensional coordinates with reference to the known coordinates ofeach of the subset of satellites to which it determined pseudorangemeasurements. Based on straightforward geometric consideration (i.e.,intersections of spheres) four pseudorange measurements are sufficientto uniquely determine the coordinates of the receiver. Threemeasurements are sufficient to determine that the receiver is at one oftwo possible points, and typically, only one of the points is reasonable(e.g., it is on the surface of the earth rather than in outer space).Using three pseudorange measurements, a GPS receiver can determine atwo-dimensional location on the surface of the earth with an accuracy ofapproximately 100 meters.

The pseudorange measurements are not, however, completely accuratemeasurements of the distance from the receiver to the satellites due toseveral factors. First, signal propagation speed from a satellite to aGPS receiver can vary due to variations in atmospheric conditions. Also,the transmitted signals are intentionally manipulated by introducingvarying time delay at the transmitter in order to limit the accuracy oflocation estimates based solely on the pseudorange measurements at thereceiver.

As a method of overcoming the inaccuracies in the pseudorangemeasurements, differential GPS (DGPS) is used. Differential GPS is basedon receiving signals from GPS satellites at a receiver that is at aknown location. The difference between a pseudorange measurement from asatellite to that receiver and a computed distance between the locationof the satellite and the location of the receiver is a pseudorangecorrection term for that satellite. Separate pseudorange correctionterms are computed for each satellite. To the extent that propagation isslowly varying and the intentionally introduced delays are also slowlyvarying, a pseudorange correction term for a satellite can be used tocorrect further pseudorange measurements from that satellite for a shortperiod of time relative to the rates of variation, for example for oneminute. Also, to the extent that variations in propagation speed are notgeographically local, a pseudorange correction term can be applied at aGPS receiver that is at a different location than the GPS receiver atwhich the correction term was computed.

In the vehicle information system, three approaches to differential GPScorrection are used. A first approach is generally known as “invertedDGPS.” In this approach, an in-vehicle system sends the pseudorangemeasurements, or other raw GPS data that is related to the pseudorangemeasurements, that it obtains from its GPS receiver to the server systemover the cellular telephone link. The server system applies thedifferential correction terms it previously obtained from its own GPSreceiver to the received pseudorange measurements it receives from thein-vehicle system and the server system calculates a corrected locationfor the vehicle.

In a second approach to GPS location estimation, the server systemtransmits pseudorange correction data to an in-vehicle system. Thein-vehicle system provides the received correction data to its GPSreceiver which then outputs improved location estimates based on its rawpseudorange measurements and the pseudorange correction data.

A third way that differential GPS is used in the system is for anin-vehicle system to determine its own pseudorange correction data basedon its own location estimate. For instance, when an in-vehicle systemdetects that the vehicle is at a known maneuver point along a plannedroute, it computes the pseudorange correction data based on thedownloaded location of the maneuver point. The differential correctiondata is then used for a period of time after the maneuver point ispassed.

An alternative mode of correction of GPS location estimates computed bythe in-vehicle system uses correction data in terms of differences inlatitude and longitude rather than differences in pseudorangemeasurements. For instance, the server system can provide GPS correctiondata that includes an offset in latitude and in longitude that thein-vehicle system adds to the latitude and longitude location estimatesoutput from its GPS receiver. If this type of GPS correction is used,the in-vehicle GPS receiver does not have to have a differential GPScapability since the location correction is performed on the output ofthe GPS receiver, rather than as part of the process of computing alocation estimate in the GPS receiver.

2.5 In-vehicle Software Components (FIGS. 4A-B)

Referring to FIGS. 4A-B, software components of in-vehicle system 105which execute on onboard computer 210 (FIG. 2) include relatively staticdata stored in static storage 222, and code stored in working storage410, which is made up of some combination of DRAM 220 and EPROM 218shown in FIG. 2.

Static data includes in-vehicle database 432 and software 436. Code inworking storage 410 includes a navigation application 412, acommunication interface 414, and a vehicle interface 416. Communicationinterface 414 provides an interface between navigation application 412and GPS receiver 252 and cellular transceiver 254. Vehicle interface 416provides an interface between navigation application 412 and sensors230, vehicle systems 270, and I/O devices 240.

2.5.1 In-vehicle Database 432 (FIGS. 11-14)

In-vehicle database 432 is used by in-vehicle system 105 for twoprinciple functions. First, in-vehicle system 105 uses in-vehicledatabase 432 in the destination specification phase in which thedatabase is used to determine alternatives to present to the operator,and to validate inputs from the operator. Second, in-vehicle system 105uses in-vehicle database 432 during the guidance phase when thein-vehicle system detects that the vehicle is off route and it must plana new route.

For the destination entry phase, database 432 includes tables that areused by the in-vehicle system to determine the names of known cities,the street names of streets in those cities (including residential, orside, streets), and the valid street address numbers on those streets.The database also includes tables that specify types of points ofinterest, and the points of interest of a particular type near avehicle's location or in a particular city.

For the guidance phase, database 432 includes additional tables that thein-vehicle system uses to plan a route from a determined location(latitude and longitude) to a desired destination or an intermediatepoint on a previously planned route. For instance, the main roadsnetwork 1000 (FIG. 10) is stored in data tables in in-vehicle database432.

Referring to FIG. 11, an AddressCityState table 1110 in in-vehicledatabase 432 includes a series of records that associate (Country,State, City) combinations with a series of (Street, Address Range)combinations. A typical record 1112 in AddressCityState table 1110includes a Country field 1114 that references the name of a country in aCountry table 1120. Country table 1120 holds the text representations ofthe names of known countries, such as “United States” or “Canada.”Record 1112 also has a CityState field 1116 which is a reference to aCityState table 1130 that is used to determine the text representationof a city and state in the country referenced by Country field 1114.Record 1112 also includes an AddressStreet field 1118 that referencesthe first of a range of records 1158 in an AddressStreet table 1150.Directly after record 1112 in AddressCitystate table 1110, a record 1113includes an AddressStreet field 1119 that references the next record1153 after range 1158, thereby defining the records in range 1158.

Each record in AddressStreet table 1150 is associated with a combinationof a complete street name, and a range of valid street numbers for thatstreet name. Multiple records in AddressStreet table 1150 can refer tothe same street name in order to build up an entire range of validstreet numbers. A typical record 1152 in AddressStreet table 1150includes a Streetname field 1154 and an AddressRange field 1156.Streetname field 1154 references a record in a StreetRecord table 1160that is used to form the text representation of the street name.AddressRange field 1156 references a record 1182 in AddressRange table1180 that includes entries for the lowest 1184 and highest 1186numerical values in a valid range of the street numbers for theassociate street.

StreetRecord table 1160 is used to form completely specified streetnames in terms of base street names, optional prefixes and suffixes, andstreet types. For instance, “North Main Blvd” is represented by the basestreet name “Main,” the prefix/suffix combination “North/-” and thestreet type “Blvd.” A typical record 1162 in StreetRecord table 1160includes a StreetName field 1164 that references the text form of thebase street name stored in a StreetName table 1170, and an AffixTypefield 1166 that includes a representation of the prefix/suffixcombination as an index to the predetermined set of prefix/suffixcombinations and a text representation of the street type.

Referring back to record 1112 in AddressCityState table 1110, CityStatefield 1116 references a record 1132 in CityState table 1130. Record 1132includes a City field 1134 that encodes the text representation of thename of the city, and a State field 1136 that references a record 1142in a State table 1140 that encodes the name of the state.

Several tables shown in FIG. 11 store lists of text names. These includeCountry table 1120, StreetName table 1170, State table 1140, andCityState table 1130. In FIG. 11, references to records are shown asproviding a direct access to the stored text representations. Referringto FIG. 12, a representative text table 1200 includes an index 1210 anda compressed text region 1220. A reference to a particular record isused as an offset to a record 1212 in index 1210. Record 1212 includes astarting field 1214 and a length field 1216. Compressed text 1220includes the concatenation of all the text records, encoded as asequence of 6-bit character representation. Starting field 1214 is theindex of the starting 6-bit character of the record. In order for aprocedure executing on onboard computer 210 to access the text string,the procedure first converts the index to the address of the starting8-bit byte of storage, and then it unpacks the 6-bit characterrepresentation to form a standard 8-bit character representation of therecord.

Referring to FIG. 14, an additional set of tables supports entry of adestination in terms of a “point of interest” (POI). Points of interestare divided by type, such as “restaurants,” “ATM machines,” and “gasstations.” A POIType table 1410 includes a sequence of records. Atypical record 1412 in POIType table 1410 includes a Type field 1414that references a record 1422 in a POITypes table 1420. Record 1422 is atext representation of the type of POI.

Record 1412 of POIType table 1410 includes an Offset field 1416 thatreferences a first record 1432 of a range 1444 of records in aPOINameCity table 1430. An Offset field 1417 of a record 1413 thatimmediately follows record 1412 in POIType table 1410 references arecord 1446 in POINameCity table 1430 that immediately follows range1444 of records in POIType table 1410.

Record 1432 in POINameCity table 1430 includes a Country field 1434,which references a record in Country table 1120 (FIG. 11), a CityStatefield 1436, which references a record in CityState table 1130, a POINamefiled 1438, and an Offset field 1440, which references a record 1452 ina POIList table 1450 which is the first record in a range 1464 ofrecords in POIList table 1450 associated with record 1432. An Offsetfield 1440 of a record 1433 that immediately follows record 1432 inPOINameCity table 1430 references a record 1466 that immediately followsrange 1464 in POIList table 1450.

Record 1452 in POIList table 1450 includes a StreetName field 1454,which references a record in StreetRecord table 1160, an Address field1456 that encodes the street number associated with the address of thepoint of interest, a PhoneNumber field 1458 which encodes the telephonenumber of the point of interest, and a Latitude/Longitude field 1460which encodes the latitude and longitude of the point of interest.

Additional tables are included in in-vehicle database 432 to supportother forms of destination specification. In versions of the system thatsupport destination specification in terms of a “Yellow Pages”(telephone directory) category, in-vehicle database 432 includes a texttable of “Yellow Pages” categories. In versions of system that supportdestination specification in terms of a pair of intersecting roads, atable of valid cross-street combinations is included in in-vehicledatabase 432. If a table of cross-street combinations is included, thetable can alternatively include only intersections of main streets, oradditionally include intersections of main streets and smallerresidential streets, or even intersections of pairs of residentialstreets, if sufficient storage is available in the in-vehicle system.

Additional tables in in-vehicle database 432 (FIG. 4) are used duringthe guidance phase when the vehicle is determined to be off route. Inparticular, these tables encode main roads network 1000 (FIG. 10).Referring to FIG. 13A, a representative link of main roads network 1000joins a node i 1301 and a node j 1302. Link c 1307 joins nodes i 1301and j 1302. Link c 1307 includes two shape points 1303 and 1303. Node i1301 is also connected to links a 1305 and b 1306 and node j 1302 isalso connected to links d 1308 and e 1309.

Referring to FIG. 13B, several tables are used to represent the mainroads network 1000. Records in these tables related to therepresentative link shown in FIG. 13A are illustrated in FIG. 13B. AMasterNode table 1310 includes one logically variable length record foreach node in the network. A record 1312 which is associated with node i1301 includes a Latitude/Longitude field 1314 that encodes the locationof node i 1301. Record 1312 also includes a set of link fields 1316, onefor each of the links joined at node i 1301. Each link field 1316includes information related to allowable turns from that link ontoother links at that node, and includes a reference to a record in aLinkSegments table 1330 associated with that link. For instance, thelink field 1316 associated with link c 1307 references record 1332 inLinkSegments table 1330.

Record 1332 in LinkSegments table 1330 includes a StreetName field 1334,which references a record in StreetRecord table 1160, and a referencenode field 1336 and a non-reference node field 1338 which referencerecords 1312 and 1318 in MasterNode table 1310, respectively. Record1332 also includes a ShapePointInfo field 1340 which references a record1352 in a LinkShapePoint table 1350. The record referenced byShapePointInfo field 1340 includes information related to the shapepoints on the link, as well as information related to signs on the link.Record 1332 also includes a Class field 1342, which encodes the roadclass of the link, and an AddressRanges field 1344, which references tworecords in AddressRange table 1180, one for each side of the road.

Record 1352 in LinkShapePoint table 1350 includes a NumberShapePointsfield 1354 and a NumberSigns field 1356. For each shape point, record1352 includes an encoding of the change in latitude and longitude fromthe previous shape point, or from the reference node for the first shapepoint. Record 1352 also includes SignInformation 1360 describing thesigns that would be seen by someone driving along the link.

2.6 Server Software Components (FIG. 5)

Referring to FIG. 5, server system 125 includes software that executeson server computer 310 (FIG. 3). This software includes a navigationapplication 512, which is used to interact with the in-vehicle systems.Navigation application 512 is coupled to a communication interface 514,which is used to communicate with telephone interface 320 (FIG. 3).Navigation application is also coupled to a GPS interface 516 that iscoupled to GPS receiver 325 (FIG. 3).

Navigation application 512 also makes use of a number of databases thatit accesses through a data interface 518. Server system 125 includes aserver map database 520 that includes the complete road network 700(FIG. 7). This database is derived from map information 360 providedfrom map provider 160. The map information is processed by a mapprocessor 550 that reformats the map information to form server mapdatabase 520. The same map information is used to derive the mapinformation that is stored in the in-vehicle databases 432 in thevehicles. Map processor 550 can be implemented as a software module thatexecutes on server computer 310, or can alternatively execute on someother computer allocated to the reformatting task. By deriving both theserver map database and the in-vehicle map database from the same mapinformation, consistency between the in-vehicle and the server data isguaranteed.

Navigation application 512 also makes use of a yellow pages database 522that it uses to convert the telephone number of a desired destination toa street address in a “reverse” number lookup. The information needed toconstruct yellow pages database 522 is provided by an externalinformation system 130, such as a telephone company or a publisher oftelephone directories.

Navigation application 512 also makes use of a traffic database 524.Information in traffic database 524 includes typical link speeds that ituses for route planning. The information comes from a combination of anexternal information system 130, such as from a government run trafficmonitoring authority, and from logging data obtained from probe vehicles(see Section 3.5). If probe vehicles are used to collect trafficinformation, then traffic information can also be provided by the serversystem to the external traffic information system.

3 System Operation FIGS. 15A-B and 16-18

3.1 General Procedure

System operation involves cooperation between in-vehicle system 105 andserver system 125 (see FIG. 1). The procedure followed from the time atwhich an operator of a vehicle begins specifying a destination to thetime at which the vehicle reaches the specified destination isillustrated in the pseudocode listing in FIGS. 15A-B and 16-18.

Referring to FIG. 15A, the procedure followed by in-vehicle system 105(FIGS. 1, 2) from the time at which the operator begins specifying thedesired destination to the time that the in-vehicle system can beginguiding the operator to the destination shown. The in-vehicle systemfirst accepts a destination specification from the operator (line 1502).This can take several separate interactions with the operator, forinstance the operator selecting a city, then a street, and then a streetnumber. Various types of destination specification procedures aresupported by the system, as described further below (see Section 3.2.1)

The in-vehicle system also determines the vehicle's initial location ordata related to the vehicle's initial location, and in some versions ofthe system the orientation of the vehicle (line 1503). The location orlocation-related data includes one or more of (a) a GPS locationestimate or pseudorange measurements obtained at the time that thenavigation request is being made, (b) past GPS-based location estimates,and (c) dead-reckoning from previous GPS-based location estimates orfrom maneuver locations. Starting location estimation is discussedfurther below (see Section 3.2.2)

After having accepted the destination specification from the operator,and location data related to the vehicle's current location, thein-vehicle system establishes a communication session with the serversystem (line 1504). The in-vehicle system establishes the communicationsession by making a cellular telephone call to the server system andthen establishing a data communication session with the server systemusing its modem.

The in-vehicle system then sends the location data and the destinationspecification to the server system (line 1505).

Referring now to FIG. 15B, the server system accepts the communicationsession from the vehicle (line 1552) and receives the location data andthe destination specification (line 1553).

The server system receives signals from multiple GPS satellites 140 andcomputes GPS correction data for each of the satellites (line 1554). Theserver system then determines the vehicle's location (line 1555). Indetermining the vehicle's location, if the in-vehicle system providedraw GPS data, such as pseudorange measurements to GPS satellites 140,the server system applies the GPS correction data it has computed to theraw GPS data that the vehicle provided to compute the vehicle'slocation.

In alternative versions of the server system, the server's GPS receiver(or at least its GPS antenna) is not necessarily located at thecentralized server. For instance, the centralized server can be somedistance from the vehicles. The GPS receiver and antenna are locatednearer to the vehicles than the centralized server. This makes the GPScorrection data more accurate since the server system's GPS receiver isthen closer to the vehicles at which the GPS location estimates arebeing estimated. Also, a server system can have multiple GPS receiversin different locations. The server system then chooses the closest GPSreceiver to a vehicle for which it is providing correction data. In thisway, a single server system can service vehicles in a wide geographicarea over which common GPS correction data may not be effective duegeographic variations in the correction terms.

For certain types of received destination specifications, and inparticular, a destination specification in terms of a class of “yellowpages” categories, the destination is not fully specified at this point.If this is the case (line 1556) then further operator input may berequired in response to secondary specification data provided by theserver system. The server system sends the secondary data to the vehicle(line 1557). For instance, if the operator specified the destination interms of a yellow pages category, the server system provides secondarydata with the specific listings in that category that are near thevehicle's location.

Referring back to FIG. 15A, the in-vehicle system accepts the secondarydestination specification data (line 1507). Using this data, thein-vehicle system presents the data to the operator and accepts asecondary destination specification from the operator, for instance as achoice from the list of destinations defined in the secondaryspecification data. The secondary destination specification is sent tothe server (line 1509). At this point, the server system has acompletely specified destination.

Turning back to FIG. 15B, the server system now determines a route (seeSection 3.2.4) from the vehicle's location to the specified destination(line 1561). The server system also determines a spot map around thevehicle's location that it will download to the vehicle (line 1562). Theserver system also determines whether to download spot maps aroundmaneuver points, for instance, based on the complexity of the maneuvers,and determines the spot maps around those maneuver points.

The server system sends the planned route, the spot map, and the GPScorrection data to the in-vehicle system (line 1563).

Referring back to FIG. 15A, the in-vehicle system receives the plannedroute, spot map, and GPS correction data from the server system (line1512) and closes the communication session with the server (line 1513).

Referring now to FIG. 16, the vehicle is now prepared to guide theoperator in a startup maneuver from its initial location onto theplanned route. First, the in-vehicle system initializes its estimatedlocation. The server system provided GPS correction data that thein-vehicle system provides to its GPS receiver in order to increase theaccuracy of the location estimates provided by its GPS receiver. The GPScorrection data that the server system provided is only valid for ashort time. After an interval of approximately one minute from the timethe GPS correction data was obtained by the server system from its GPSreceiver, the in-vehicle system stops using the correction data and usesstandard GPS instead. As is discussed further below, GPS correction datamay be obtained at other times during a trip, and in such cases, thein-vehicle system provides the correction data to its GPS receiver for afixed interval from the time that the data was generated by a GPSreceiver.

During the startup maneuver, which is the initial portion of the tripuntil the vehicle is following the planed route, the in-vehicle systemtracks the location of the vehicle using the differential GPS locationestimates until the GPS correction data is too old, and then tracks thevehicle using uncorrected GPS location estimates (line 1604). Thein-vehicle system displays the spot map along with an indication of thevehicle's estimated location and a representation of the planned route(line 1605). When the in-vehicle system detects that the vehicle isfollowing the planned route, the startup maneuver phase is completed anda turn-by-turn route following phase begins.

Referring now to FIG. 17, the route following procedure is based onnotifying the operator of each of the links along a planned route. Whiletraveling along the route, the in-vehicle system maintains two locationestimates for the vehicle. The first is based on GPS estimates, or onDGPS estimates if current GPS correction data is available. The secondlocation estimate is based on a “dead reckoning” procedure. Thisprocedure assumes that the vehicle is properly following the plannedroute. The dead reckoning uses the locations of the maneuver and waypoints along the planned route and information from the vehicle sensors,in particular, from the velocity sensor, to update this second locationestimate. If the vehicle is truly following the route, then the twolocation estimates should remain close to one another. Note that thisdead reckoning procedure does not need to use heading estimates to trackthe vehicle's position since the vehicle is assumed to be travelingalong the planned route.

Along each link, after the initial maneuver at the starting node of thelink, the in-vehicle system initializes an off-route tolerance. Thistolerance is the allowable disparity between the GPS and the deadreckoning location estimates. The tolerance grows from an initial valueestablished right after a maneuver to account for a growing inaccuracyin the estimates, due, for instance, to calibration inaccuracies in thevelocity sensor and aging of the GPS correction data. The off-routetolerance is initialized to 150 feet and grows linearly to a maximum of500 feet at a rate of about 1 foot per 100 feet traveled

While traveling to the next maneuver point (loop starting at line 1704),the vehicle increases the off route tolerance (line 1705), tracks itsdead reckoning position (line 1706), and tracks its GPS or DGPS position(line 1707) (depending of whether current GPS correction data isavailable).

If at any time the difference between the dead reckoning position andthe (D)GPS based position is more than the off-route tolerance, then aoff-route routine is initiated (line 1710).

While traveling along a link, the vehicle eventually reaches a pointnear the next maneuver. When the vehicle is estimated to be within adistance window of the next maneuver, then the operator is notified bythe in-vehicle system using graphical and aural output of the upcomingmaneuver. The size of the notification window depends on the road classbeing traveled on, which is related to the time prior to a maneuver thatan operator is notified of the maneuver. For instance, on a highway, anoperator is notified of a maneuver, such as exit from the highway, at afarther distance from the maneuver that the distance than from amaneuver in a residential neighborhood.

Also while traveling along the link, the in-vehicle system attempts todetect the precise point at which the next maneuver is carried out. Whenthe vehicle is within a distance window of the next maneuver, thein-vehicle system attempts to detect the maneuver. For instance, if themaneuver involves making a right angle turn, the signals from thein-vehicle sensors, such as from a magnetic compass or a rate gyroscope,or from successive GPS location estimates from which changes indirections are detected, provide a clear indication of the maneuverpoint.

If a maneuver is detected (line 1718) then the in-vehicle system updatesits dead reckoning location estimate based on the location of themaneuver (line 1719). Also, the in-vehicle system uses the downloadedlocation of the maneuver point to compute its own GPS correction data(line 1720). In particular, the in-vehicle system computes the deviationin latitude and longitude at the maneuver point and applies thesedeviations as corrections to the latitude and longitude positionestimates output from its GPS receiver for a one minute interval afterthe maneuver. Alternatively, the in-vehicle system uses the location ofthe maneuver point and the pseudorange measurements obtained by thevehicle's GPS receiver at the time of the detected maneuver to computenew GPS correction data that are used for a one minute interval afterthe maneuver.

Note that there are times when a maneuver is not detected, for instanceif it involves only a slight turn that is not accurately detected usingthe vehicle sensors. In such a case, the in-vehicle system continues thedead reckoning procedure under the assumption that the vehicle hasstayed on route. Such maneuver points that are not detected areessentially treated in the same way as way points from the point of viewof tracking the dead reckoning location of the vehicle.

The route following procedure continues from link to link along theroute until the destination is reached (line 1725).

Referring now to FIG. 18, the off-route routine first involves adead-reckoning position correction procedure (lines 1802-1810). If forthe direction of travel matches the planned route for an interval, forinstance, of 75 feet after the difference between the position estimateswas detected, then the dead reckoning position is updated to be theclosest point along the planned route to the (D)GPS position estimate(lines 1804-1805). In this way, if the deviation in position estimatesis due to inaccurate tracking of the distance along the route, thelocation correction procedure should successfully overcome the error. Ifthe deviation between the (D)GPS estimate and the dead-reckoningestimate is now less than the off-route tolerance, the in-vehicle systemresumes the route following procedure (line 1808). If on the other hand,even the closest point on the planned route is still more than theoff-route tolerance from the (D)GPS position, then the locationcorrection procedure is not successful and a route replanning procedureis initiated.

Referring still to FIG. 18, the route replanning procedure involvesfirst estimating the vehicle's location on main roads network 1000 (FIG.10) that is stored in the vehicle. The GPS location estimate is used tofind a link along which the vehicle is traveling (line 1811).

Once the vehicle has been located on the main roads network, thein-vehicle system calculates a best route that leads to one of themaneuver or way points along the previously planned route (line 1813).

The newly planned route to the maneuver or way point on the previousroute, along with the remaining portion of the previously planned routethen becomes the new planned route which replaces the previous one (line1815). The link-by-link route following procedure is then reentered(line 1816).

Specific aspects of the general operation of the system are described inthe following sections. These aspects includes route planning, includingin-vehicle destination specification as well as computation of the bestroute at the server system. The specific aspects also include theguidance operations carried out by the in vehicle system, as well asroute replanning operations carried out by the in-vehicle system when itdetects that the vehicle is off route. In addition, operation of thesystem in which the fleet of vehicles is used to collect traffic relateddata is described below.

3.2 Route Planning (FIGS. 15A-B)

Route planning involves several steps, as shown in FIGS. 15A-B. Inparticular, the route planning operation includes:

Destination specification (line 1502, FIG. 15A)

Starting location determination (line 1503, FIG. 15A)

Querying the server system (lines 1504-1510, FIG. 15A; lines 1552-1560,FIG. 15B)

Route planning (line 1561, FIG. 15B)

Route and spot map downloading (lines 1562-1563, FIG. 15B, line 1512,FIG. 15A)

Specific operations carried out by the in-vehicle and server systems ineach of these steps are described in the following sections.

3.2.1 Destination Input

As shown in FIG. 15A (line 1502), the first phase of navigation to adesired destination is destination input by the operator of the vehicle.In-vehicle system 105 (FIGS. 1, 2) enables the operator to specify adestination in a number of different ways. In general, the in-vehiclesystem uses in-vehicle database 432 (FIG. 4) to provide alternative inscrolling lists from which the operator chooses. A destinationspecification can be one of:

A street address (e.g., city, street, and number),

A point of interest (e.g., city, type of point of interest, and aselection from a list),

A “yellow pages” listing (e.g., type of listing, and a selection from alist),

A telephone number of the destination,

A pair of cross streets,

A selection from a list of recently specified destinations, and

A selection from a list of previously stored destinations in a user's“profile”.

In an initial interaction with the system, the operator first specifieswhat method of destination input will be used, for example, by selectingfrom a displayed list of choices.

3.2.1.1 Street Address Specification

One way that the operator can specify a destination is by the streetaddress of the destination. The destination specification in this caseis a fully specified (country, state, city, street, number) combination.The user does not necessarily have to enter each of these fields inturn. For instance, the current (i.e., previously used) country andstate can be used as defaults.

Alternative sequences of field specifications can be used. In onesequence, the operator first selects a city from a scrolling list ofcities in the current (country, state). Referring to FIG. 11, the listof valid states is obtained from CityState table 1130. After theoperator selects a desired city, the in-vehicle system presents ascrolling list of valid streets names in that city. The list of validstreet names is obtained using AddressCityState table 1100, andassociated AddressStreet table 1150, StreetRecord table 1160, andStreetName table 1170. After the operator selects a desired street, theoperator enters a street number. The in-vehicle system validates thenumber using AddressStreet table 1150 and AddressRange table 1180.

In the above procedure, alternative methods of selecting from lists ofvalid names can be used, including scrolling through a list using “up”and “down” buttons, and spelling a prefix of the name until itunambiguously specifies a full name. An alphanumeric keyboard is notnecessarily provided with this system. If one is not provided, theoperator enters letters of a spelling, or digits of a street address, bymoving a cursor to a display of the desired letter or digit andselecting that letter or digit.

There are times when the city of the desired destination is not known.In that case, the city can be initially left unknown. The list of validstreet names presented to the operator by the in-vehicle system is thenall the streets in the current state. After the street name is selected,if the city is ambiguous, the operator selects from the list of possiblecities and then proceeds to input the street number. Alternatively,disambiguation of the city of a destination street can be left untilafter a street number is also specified.

3.2.1.2 Point of Interest Specification

In specifying a destination by a point of interest (POI), the operatorfirst selects from a list of types of points of interests. Examples oftypes of POIs include banking locations, gas stations, hospitals, andrestaurants. Referring to FIG. 14, the list of valid types is obtainedby the in-vehicle system from POITypes table 1420.

The operator can select a particular POI of the selected POI type in anumber of ways. In a first way, the operator next selects a city inwhich to find the destination POI. Using POINameCity table 1430, thesystem displays a list of names, addresses and phone numbers of POIs ofthe selected type in the selected city. The operator then selects fromthe list of displayed POIs. The phone number can be useful, forinstance, if the operator wants to call the destination, such as arestaurant, before deciding to travel to the destination.

Rather than specifying the city, the system can display the POIs bytheir proximity to the current location of the vehicle. The GPS-basedlatitude and longitude estimates are compared to the Latitude/Longitudefield of records in POIList table 1450, for POIs of the selected POItype. The in-vehicle system then displays the POIs in order of proximityto the current location rather than alphabetically.

3.2.1.3 “Yellow Pages”

In order to support an operator specifying a destination to thein-vehicle system using “yellow pages” listings, the in-vehicle database432 does not have the capacity to include all the possible listings thatan operator may be looking for. Instead, only the categories of listingsare included, for example, “jewelry stores.” The in-vehicle system firstdisplays a list of categories from which the operator selects aparticular category. The operator then selects a particular destinationcity, or requests listings in the proximity of the current location. Thein-vehicle system presents a list of categories to the operator and theoperator selects from the list. Note that the destination is notcompletely specified at this point since a particular destination (i.e.,a street address) has not yet been determined.

After the communication session with the server is established, theserver downloads the specific listings in the selected yellow pagescategory to the in-vehicle system, either according to the selectedcity, or according to the proximity to the vehicle's location. Theoperator then selects from the downloaded list.

3.2.1.4 Other Destination Specifications

Several optional ways of specifying a destination can also be supportedby in the in-vehicle system.

An operator can specify a destination by selecting a pair of crossstreets. To support selection of a pair of cross streets, in-vehicledatabase 432 includes a table of valid pairs of main streets, andpossible pairs of main and side streets or even pairs of side streets.The operator selects a first street. A list of valid cross streets arethen displayed and the operator selects one from the list.

As in destination specification by street number, if the city is notspecified before specifying the cross streets, the city is disambiguatedafter one or both of the street names are selected.

An operator can specify a destination by specifying the telephone numberof the destination. A complete telephone directory is not stored inin-vehicle database 432, therefore, the validity of the telephonenumber, other than perhaps the validity of the area code, is notverified before the in-vehicle system establishes the communicationsession with the server system. The server system receives the telephonenumber and looks in up in a “reverse” telephone directory to determinethe street address of the destination.

As is described further below, individual operators can have storedprofiles that are stored in the vehicle and may have correspondingstorage on the server system. This profile can hold typicaldestinations, such as “work,” “home,” “airport,” etc. for which theoperator has previously specified particular locations.

An operator can specify a destination by selecting from the mostrecently specified locations. For example, the operator may be returningto a recently visited work site.

Alternative versions of the system allow specification of a destinationby street address, but the in-vehicle system does not have data withwhich to validate the address ranges for the specified street. Forinstance, the in-vehicle system may not have the capability to validateany street numbers, or the destination may be outside a geographic rangefor which it has stored address range data. If the in-vehicle systemcannot validate the street address, it nevertheless establishes acommunication session with the server computer. The server computer thencompletes the validation procedure.

3.2.2 Starting Location Determination

The in-vehicle system sends to the server system either an estimate ofits position, or sends raw GPS data from its GPS receiver from which theserver system computes the vehicle's position (line 1503, FIG. 15A).

There are situations in which the vehicle cannot receive signals fromthe GPS satellites at its starting location. For example, this would bethe case if the vehicle were in an underground garage. In such a case,the vehicle relies on location estimates that the system made prior toreaching the starting location. Furthermore, after a GPS receiver isfirst powered on, there can be a significant interval before which itcan provide location estimates. For example, the GPS receiver mustlocate each of the satellites that are in range, and compute theirlocations in orbit.

The in-vehicle system therefore maintains a history of GPS locationestimates on an ongoing basis, even when the operator is not beingguided along a route. This history is stored in a non-volatile memory inthe in-vehicle system before the system is shut off. Therefore, if GPSsignals cannot be received at the starting location, the latest GPSlocation estimate in the stored history is used.

In addition to sending location related data to the server system, thein-vehicle system also sends speed and orientation data. The orientationcan be obtained from either past consecutive GPS location estimates, orfrom the magnetic compass. The speed and orientation information is usedby the server system, for example, to disambiguate which of a number ofnearby road segments the vehicle is on based on the class of roadsegments and the allowable directions of travel on those segments.

If the vehicle was guided to the starting location during a previousnavigation session, the starting location can be based on dead reckoningalong the previously planned route.

Once the server system provides GPS correction data to the in-vehiclesystem, the in-vehicle system updates its starting location using theGPS correction data (line 1602, FIG. 16). For instance, if the GPScorrection data is pseudorange correction data, the in-vehicle systemprovides the pseudorange correction data to its GPS receiver andreceives the corrected position estimate from the GPS receiver. If theGPS correction data is offsets in latitude and longitude, the in-vehiclesystem applies these offsets to the estimated position output from itsGPS receiver.

3.2.3 Server Query

When the in-vehicle system establishes a communication session with theserver system (line 1504-1510, FIG. 15A), it does so in two steps. Firstthe in-vehicle system establishes a cellular telephone connection to theserver system, and then it establishes a modulated data session on thecellular telephone connection.

In the first step, the cellular telephone connection is established bythe in-vehicle system dialing a specific number to reach the serversystem. The in-vehicle system can handle typical error conditions thatmight be found in an analog cellular telephone network, such as beingout of range of the cellular system, or the cellular system not havingthe capacity to establish the call.

In the second step, once the telephone connection is set up, thein-vehicle system attempts to establish a data connection with theserver system. Typical modems carry out a negotiation phase in whichcompatible modulation, compression, and error correcting protocols areselected. In order to reduce the time needed to set up the communicationsession, a particular set of protocols is preselected, for example asthe “lowest” common protocol that all vehicles support. The serversystem expects communication using this lowest protocol. This allowsdata to flow as soon as possible without waiting for the protocolnegotiation phase to be completed. Since the amount of data to betransferred is relatively small, the time taken in negotiating the bestprotocols would likely be larger than the time saved by sending the datausing the negotiated protocol rather than with the preselected protocol.

3.2.4 Route Planning

Route planning at the server system (line 1561, FIG. 15B) uses wellknown route finding approaches. In particular, two instances of thewell-known A* (“A-Star”) graph search algorithm are used in conjunctionwith road network 700 (FIG. 700). One instance of the A* algorithmstarts at the starting location and one starts “backwards” from thedesired destination. The A* algorithm is a type of “best first” searchapproach. At any point executing the algorithm, the actual distancealong the graph from an initial node to a set of intermediate nodes hasbeen computed. A lower bound (or in some versions of the algorithm, anestimate) of the distance from each of the intermediate nodes to thefinal node is added to the actual distance. The intermediate node withthe lowest sum is extended. If the lower bounds are used, this algorithmproduces the shortest path from the initial node to the final node.Using the two instances of the A* algorithm, a best path is chosen afterthere are intermediate nodes in common for the two instances of thealgorithm.

Alternatives to the A* route planning algorithms can be used. Forinstance, Dijstra's algorithm, or another type of best first algorithmcan be used.

Route planning can be based on a variety of criteria. A shortest totaldistance uses the actual link distances in the road network to determinethe cost of a path. The lower bound on the remaining path can bestraight-line distance between an intermediate node and the final node.Route planning can alternatively be based on lowest expected traveltime. Travel time along a link can be based on an expected speed fordifferent road classes, or can be based on specific speed data stored onthe server system and associated with particular links. For example, theserver system may know that certain links are congested with slower thanexpected speeds for their road classes. The route planning algorithmwould then tend to avoid such a congested link if there are alternativeroutes that can be taken.

Other alternative route planning approaches can also be used on theserver system. For instance, routes can be constrained to followparticular road segments, and the cost of routes can include otherfactors than distance or expected travel time, such as toll fees alongthe route.

3.2.5 Route and Spot Map Download

Referring to FIGS. 8 and 9, the server system downloads a route as asequence of links joined by maneuver points, and downloads spot maps assmall graphs around the starting location or the selected maneuverpoints (lines 1562-1563, FIG. 15B, line 1512, FIG. 15A). In order toreduce the download time needed, this data is represented as a compactdata structure.

The planned route is downloaded as a sequence of route links using acompressed format. For each link in the planned route, the downloadedinformation includes:

The latitude and longitude of the starting node (maneuver point) of thelink, encoded as 32-bit integers in units of 10⁻⁵ degrees,

Turn information, encoded as an index representing messages such as“turn right,” “keep left,” etc.,

The number of “arms” at the current maneuver point,

The number of way points before the next maneuver, and

The rank (e.g., the size or classification) of the road segmentassociated with this link.

In addition, for each way point, the data for a link includes:

The change in latitude and longitude from the previous way point, orfrom the starting node for the first way point, encoded as 12-bitintegers in units of 10⁻⁵ degrees.

Note that 12 bit encoding of the change in latitude or longitude limitsthe change to approximately 2^(12×10) ⁻⁵=0.04 degrees. If a segment ofthe route planned by the server system includes a greater change betweensuccessive maneuver or way points, the server system inserts additionalway points that are sufficiently close to encode the changes in the12-bit quantities.

In addition, for each link, the downloaded data includes:

The length of text fields, if any, associated with the name of thestreet associated with the link, and the name of the street to be turnedonto at the next maneuver point, and with any signage or other specialinformation to be presented to the operator, and

The text fields themselves.

For each “arm” at a maneuver point, the downloaded data includes datarelated to the angles at which the intersecting streets join at themaneuver point, thereby allowing a relatively accurate graphicalrepresentation of the maneuver to be displayed to the operator.

This route download format provides a compact representation that can bedownloaded quickly from the server to the vehicle. Alternative versionsof the system can take advantage of data in the in-vehicle database toreduce the amount of data still further, for example, by referencingstored street names or by using references to nodes in the main roadsnetwork that is already stored in the vehicle. Alternative versions ofthe system can also include additional information related to the links.For example, link travel speeds can be downloaded, particularly if thelinks are known by the server to be exceptionally congested.

An alternative approach to route downloading includes use of predefinedsequences of road segments that are stored in the in-vehicle systems.The server system replaces an sequence of road segments, maneuverpoints, and waypoints, with a reference to the stored predefinesequence. In this way, typically traveled routes, for example, along ahighway do not have to be downloaded explicitly. The server system canperiodically update the stored sequences in the vehicles to reflect thetypically requested routes by those vehicles. Alternatively, thein-vehicle system retains a memory of previously downloaded routes, andthe server can refer to portions of those routes when downloading anewly planned route.

3.3 Guidance

Guiding the operator to the desired destination involves several aspectsof operation of the in-vehicle system. These include:

A startup maneuver (FIG. 16),

Dead reckoning location tracking (FIG. 17, line 1706),

GPS location tracking and off-route detection (FIG. 17, lines1707-1710), and

Maneuver notification and detection (FIG. 17, lines 1712-1722).

These aspects are described in the following sections.

3.3.1 Startup Maneuvers

There are several reasons that an operator may not be able to follow aninitial route. One is inaccuracy of the initial location of a vehicle.For instance, the GPS may indicate that the vehicle is on a street, whenin fact it is in a nearby parking lot or an adjacent street. Also, if avehicle is pointing in the opposite direction on a street than theserver system expects, then the vehicle is likely to go off route rightfrom the very first step. Also, following directions at the start of aroute can be difficult, for instance, due to the close spacing of sidestreets, inadequate signs, distractions, traffic, etc.

For these and other reasons, the system does not rely on an operatormaking no mistakes right from the very initial starting location.Instead, the starting location is used to determine the spot map that isdownloaded to the vehicle. The spot map typically covers only two orthree intersections in any direction from the starting location. Theplanned route is shown in conjunction with the spot map, as is thevehicle's DGPS based location. The operator uses this map representationto get onto the planned route.

Once the vehicle is on a segment of the planned route, and traveling inthe correct direction, the turn-by-turn guidance phase begins.

3.3.2 Dead Reckoning Location Tracking

Once the in-vehicle system enters the turn-by-turn route following(guidance) phase, the in-vehicle system maintains a dead reckoninglocation estimate of the vehicle. In general, the in-vehicle systemtracks the vehicle under the assumption that the operator is trying tofollow the instructions. Dead reckoning is based on converting thevelocity signal from velocity sensor 232 and the straight lineapproximations of the links between maneuver or way points along theplanned route into an updated location. In particular, if the in-vehiclesystem assumes that the vehicle is at a known maneuver point, then asthe vehicle travels a distance measured according to the velocitysignal, the in-vehicle system estimates the vehicle's location as thepoint that is the measured distance along the sequence of links from themaneuver point. The locations of the nodes at the ends of each link areknown to the in-vehicle system, therefore, the in-vehicle systemessentially uses the direction of the links to estimate the directionthat the vehicle is traveling as it leaves the maneuver point, and as itpasses over subsequent links on the route.

Dead reckoning relies on a known correspondence between the velocitysignal and the distance traveled. Several factors affect thiscorrespondence, including tire pressure which is affected bytemperature, which affects the circumference of the tires. In order toimprove the accuracy by which the distance traveled is estimated fromthe velocity signal, an ongoing calibration procedure is supported. Whenthe in-vehicle system detects a maneuver, it compares the velocitysensor-based distance estimate and the map-based distance estimate. Thein-vehicle system adjusts a scale factor relating the number of velocitysignal pulses to the distance traveled so that the velocity sensor andmap-based traveled distance estimates match.

3.3.3 GPS Location Tracking and Off-route Detection

While the operator is being directed from maneuver to maneuver along theplanned route, the in-vehicle system continuously updates its GPS-basedlocation estimate while the GPS satellite signals are received. Inaddition, there are intervals during which the in-vehicle system hascurrent GPS correction data that it provides to the GPS receiver inorder to improve the accuracy of the GPS-location estimates, forinstance, in a differential correction mode.

GPS correction data is received by the in-vehicle system from the serversystem when the planned route is downloaded. In alternative versions ofthe system, there may be other times at which the server providesdifferential correction data, for instance during communication sessionsthat are established for another purpose.

The in-vehicle system can also compute its own GPS correction data whenit knows its location precisely. The in-vehicle system estimates itslocation very accurately when it detects that a planned maneuver isexecuted by the operator, since an accurate location of each maneuver isdownloaded for the server system when the planned route is downloaded.

Therefore, while negotiating the planned route, the in-vehicle systemreceives a stream of GPS or DGPS based location estimates. Theselocation estimates are compared on an ongoing basis to the deadreckoning position estimates also maintained by the in-vehicle system.

After a vehicle executes a maneuver, and in particular when GPScorrection data is computed based on the location of the maneuver pointand the raw GPS data recorded when the vehicle passes through themaneuver point, the GPS-based location and the dead-reckoning positionsshould match. As a vehicle correctly passes along the planned link, thedead-reckoning position and the GPS-based position are expected todiverge somewhat for several reasons. These reasons include increasederror in the GPS estimates, and possible map errors.

The GPS correction data is provided to the GPS receiver forapproximately one minute after the maneuver. During that time, theirutility slowly decreases, that is, the error of the DGPS based locationestimates slowly increases. After the GPS correction data is no longerused, the GPS error is expected to remain within a fixed range.

The error in the dead reckoning position estimate grows primarily due toerror in estimating the distance traveled along the links. Also maperrors, both in the length of links and the location of waypoints ormaneuver points, can contribute to a growing dead reckoning positionerror.

The combination of a growing error in each of the two terms iscompensated for by using an increasing tolerance beyond which anoff-route condition is detected by the in-vehicle system. The tolerancestarts at 150 feet. The tolerance increases at a rate of 1 foot per 100feet traveled until the tolerance reaches 500 feet.

If at any point the difference between the two location estimatesexceeds the tolerance, the in-vehicle system detects an off-routecondition it attempts to correct the dead reckoning position estimateand it that is unsuccessful, it executes a route replanning procedure(see Section 3.4).

3.3.4 Maneuver Notification and Detection

Maneuver notification and detection both use the dead reckoning positionestimate, or more particularly, use a dead reckoning estimate of thescalar distance traveled along the planned route from a previouslydetected maneuver.

The in-vehicle system gives instructions to the operator at distanceprior to when the in-vehicle system expects the vehicle to execute thenext maneuver. This accounts for both the reaction time needed by theoperator, as well as inaccuracy in the system's estimate of the distanceto the next maneuver. In order to account for the different amount oftime or distance needed by an operator to act on a command, theinstructions are given farther from the next maneuver on high-speedlinks, such as highways, than on small residential streets. Each roadclass has a fixed distance from an upcoming maneuver at which the nextinstructions are given.

The in-vehicle system also gives voice prompts as the vehicle enters thenotification window. Graphical and text prompts and instructions aredisplayed at least from the point that the vehicle enters thenotification window, and can be displayed sooner.

In a distance-based window around the point at which the in-vehiclesystem expected the next maneuver to be carried out, the in-vehiclesystem attempts to detect the exact point at which the maneuver occurs.For instance, if the maneuver involves a right angle turn, the output ofthe onboard magnetic compass or the GPS-based direction estimate is usedto reliably detect the maneuver. Also, sensing of the vehicle speed todetect certain classes of maneuvers, such as stopping at a toll booth.

Certain maneuvers cannot be detected with high accuracy. For instance, aturn may be too gradual to detect using the signal produced by amagnetic compass. If the vehicle leaves the maneuver detection windowwithout detecting the expected maneuver, then the in-vehicle systemsimply continues to update the dead reckoning position until asubsequent maneuver is detected.

3.3.4.1 Display and Voice Commands

In addition to receiving audible instructions, the maneuver notificationand instructions are provided on the in-vehicle display. The displayinclude:

A graphical illustration of the “distance to go” until the nextmaneuver, or example as a bar chart that gradually fills as the link istraversed,

A digital “distance to go,” for instance a number in miles or feet,

A graphical representation of the upcoming road geometry at the nextmaneuver, for instance showing the angles at which all roads meeting atthe next intersection joint, and

Sign text that should be visible at the next maneuver point.

Voice instructions include a variety of pre-stored phrases, includingcommands to notify a driver of an upcoming maneuver, and commands toinstruct and operator to make a maneuver at the point that theinstruction is give.

3.4 Route Replanning

When the in-vehicle system detects that a vehicle is off the plannedroute, it executes a route replanning procedure (FIG. 18). The firststep is to determine where the vehicle is traveling on the main roadnetwork 1000, which is stored in in-vehicle database 432.

The in-vehicle system uses the GPS (or DGPS) based latitude andlongitude estimates to search through the list of nodes in MasterNodetable 1310. Sequential GPS-based position estimates, or the output ofthe magnetic compass, are used to determine a direction of travel alonga link joining to adjacent nodes. This then determines which link inLinkSegments table 1330 the vehicle is traveling on, and the directionof travel along that link.

The in-vehicle system then executes a shortest path search (e.g., an A*search) starting at that link to one of the maneuver or way points alongthe planned route. A number of points, or alternatively all points, oneither side of the last maneuver point are used as points at which thereplanned route can join up with the previously planned route. Forinstance, ten points before and after the last detected maneuver pointcan be used. Limiting the number of points can reduce the amount ofcomputation (time and memory) required to replan the route. If there arefewer than ten remaining points, then the actual desired destination isone of the points that the replanned route can “join” to planned route.

As in the server system based route planning approach, the in-vehiclesystem uses an A algorithm to plan the route. The starting point isdetermined using the scanning of MasterNode table 1310, as describedabove. As intermediate nodes are considered in the A* search, the lowerbound on the distance to the desired location is minimum over themaneuver and way points near the last detected maneuver point of the sumof the straight-line distance from the intermediate point to themaneuver or way point plus the previously calculated distance along thepreviously planned route from that maneuver or way point to the desireddestination. In this way, the best point of rejoining the previouslyplanned route is found.

As in the server system based route planning, the cost of traveling overa link can be based on the length of the link, an estimate of the timeto travel over the link based on the road class of the line, or anestimate of the time to travel a link based on specific road speedinformation associated with that link.

3.5 Floating Vehicle Data Collection

Referring to FIG. 19, navigation application 512 which is part of serversystem 125 makes use of a traffic database 524 when planning routes thatare based on expected travel time. In the description of the systemabove, traffic information provided from an external information system130, such as from a government run traffic monitoring authority, is usedto populate traffic database 524.

In addition to relying on an externally provided traffic information,server system 125 makes use of some or all vehicles 100 as “probes” forcollecting traffic information. Navigation application 512 receives thetraffic information from the probe vehicles and feeds the collectedtraffic information back into traffic database 524 In addition, theserver system optionally sends updated traffic information to theexternal information system. In this way, the vehicle navigation systemcan be a source of traffic information in addition to, or instead of,being a consumer of traffic information from external information system130.

Two modes of data collection are used. First, ongoing traffic “profile”data is collected by the in-vehicle systems in probe vehicles.Occasionally, the probe vehicles upload their collected data to theserver system and the server system updates its traffic database basedon the uploaded information. In the second mode, the in-vehicle systemsin the probe vehicles detect when the vehicle's speed is significantlyslower than would be expected based on the class of road being traveled,on or based on traffic related data that is stored in the vehicle andwhich relates the expected speed to the road segment being traveled on.When the in-vehicle system detects that the vehicle's speed is slowerthat expected, that is, it detects any exception from expected trafficconditions, it immediately reports the exception to the server system sothat the server system can update its traffic database 524 to reflectsunexpected traffic conditions.

3.5.1 Traffic Profile Collection

In the first mode of traffic data collection, navigation application 412in in-vehicle system 105 of a probe vehicle collects on an ongoing basisa history (a profile) of the speed that the vehicle travels on links ofthe main roads network (or equivalently the transit times on the links).The in-vehicle system collects the traffic profile data independently ofthe guidance function. That is, the vehicle does not have to be guidedby the navigation system in order to collect traffic profile data. Thenavigation application stores the time of day and the speed traveled oneach link in a link speed log 1920.

In order to build up link speed log 1920, the in-vehicle system tracksthe vehicle's location on main roads network 1000 that is stored inin-vehicle database 432 Using the GPS location estimates it receivesfrom its GPS receiver, the in-vehicle system detects when the vehicle isfollowing a road segment (link) of the main roads network. Thein-vehicle system records the time the vehicle takes to travel from oneend to the other of the link and stores a reference to the link, thetime of day, and the speed traveled along the link in the link speedlog. As the vehicle travels over multiple links of the main roadsnetwork, a series of travel times is logged, each associated with a linkthat was traversed.

Occasionally, for example when vehicle leaves the main roads network, orperiodically, such as daily, the in-vehicle system sends the loggedprofile information it has stored in link speed log 1920 to the serversystem over a data connection that the in-vehicle system initiates overa cellular telephone connection with the server system. After it hassent the information, the in-vehicle system clears its link speed log.

The operator of the vehicle has the option of enabling or disablingeither mode of data collection through the user interface of thein-vehicle system. Also, the server system can enable (or request)either type of collection. For instance, the server system can enablemore vehicles if it needs more data, and disable data collection in somevehicles if it is receiving more data than it needs.

At the server system, navigation application 512 receives the loggedspeed information from a number of probe vehicles. Using this collectedinformation, the navigation application updates traffic database 524.For example, the navigation application incorporates the reported speedsfor a particular link into an average speed for that link that is storedin its traffic database. Optionally, the server system provides theupdated traffic information to external information system 130.

On the server system, traffic database 524 includes an average linkspeed for each link (in each direction), as well as a start and a stoptime for a morning and an evening rush “hour” (busy period). For eachbusy period, the traffic database includes the average speed during thatperiod.

Various alternative intervals can be used. For instance, equalfive-minute intervals can be used, as can unequal intervals, such as 1hour intervals in the middle of the night and five-minute intervals attypically busy periods.

Optionally, the average link speeds stored in the server system'straffic database 524 are downloaded and stored in a link speeds database1910 in the in-vehicle system of each vehicle. This link speeds databaseis used, for instance, by the in-vehicle system when replanning a routebases on a shortest expected travel time.

3.5.2 Exception Reporting

In the second mode of traffic data collection, the in-vehicle systemmakes use of information in its link speeds database 1910, whichincludes expected travel speeds for all the links in main roads network100. Multiple travel times are stored for each link, for instance, toaccount for the variations due to morning and evening busy periods. Foreach link, the following information is recorded:

Typical expected speed

Start and end times of the morning busy period

Expected speed during the morning busy period

Start and end times of the evening busy period

Expected speed during the evening busy period

Alternatively, other types of intervals can be used to store the speedinformation. Also, rather than relying on specific speed information fora link, the in-vehicle system can alternatively base the typicalexpected speed for a link on the class of the link. For instance, a linkon a class 4 (highway) link can be typically expected to be close to thespeed limit (e.g., 55 MPH).

As in the profile data collection mode, the in-vehicle system of a probevehicle tracks the location of the vehicle using GPS location estimatesas it traverses links of the main roads network, and detects when thevehicle traverses particular links in the main roads network. Thein-vehicle system detects that a traffic exception has occurred if atravel speed along a link is substantially slower or faster thanexpected (e.g. 75% of the expected speed or slower) for that link atthat time of day.

When a traffic exception occurs, the in-vehicle system establishes acommunication session with the server system by placing a cellulartelephone call to the server system. The in-vehicle system transmits ashort data message encoding the exception, identifying the link and thetravel speed, to the server system.

In an alternative approach to exception reporting, a vehicle makes aprobabilistic choice of whether to transmit the exception message. Inthis alternative, not all vehicles which encounter the exceptiontransmit to the server system, thereby reducing the communication loadon the server system.

The server system receives the exception message from the in-vehiclesystem. The server system updates traffic database 524, which it uses toplan routes, based on the exception messages it receives from the probevehicles. If there is a sufficient “density” of probe vehicles on theroad network, the server system will typically receive exceptionmessages from multiple probe vehicle. Therefore, optionally, the serversystem can require that two or more probe vehicles report an exception(i.e., a traffic exception is confirmed by another vehicle) beforeupdating its traffic database.

The server system resets its expected speeds for the links on whichexceptions have been reported after a period of time when no moreexceptions are reported by probe vehicles for those links.

Operation of the exception data collection mode does not necessarilyrequire intervention of the operator. The operator of a probe vehiclecan explicitly enable or disable exception reporting. Also, thein-vehicle system can be configured so that the operator is asked toconfirm the validity of exception information before it is sent to theserver system. For instance the in-vehicle system can display theexception message to the operator and the operator must press a buttonindicating that the message is valid before it is sent to the serversystem. This confirmation approach avoids having a vehicle report anexception when slow speed is due to a non-traffic related reason, suchas stopping for gas along the link.

In a alternative version of the system, exceptions are logged ratherthan immediately reported to the server system. The in-vehicle systemthen uploads the logged exceptions to the server system in the same waythat it can upload logged profile data.

3.6 Server Control

In an alternative version of the system, the system controls the vehicledata collection, for instance, to limit the rate at which it receivesdata from probe vehicles, or to receive data related to particularregions or roadways. Alternative methods of controlling the collectioninclude the following.

In a first alternative, the probe vehicles do not transmit their loggedspeed data unless queried by the server system. The server system polls(interrogates) vehicles to receive their logged speed data. In oneapproach, the server system polls vehicles based on the geographicregion in which the vehicles typically travel. For instance, if theserver system does not have up-to-date data for roads in a region, itpolls vehicles that typically travel in that region. To poll a vehicle,the server system places a cellular telephone call, or otherwisenotifies the vehicle, the in-vehicle system. The in-vehicle systemreceives the call and provides its logged speed data to the server. Forexample, an alternative to placing a telephone call is to broadcast amessage to a number of vehicles over a broadcast channel, such as on asideband of a commercial radio broadcast. In another approach to thisalternative, the server system polls vehicles for which it has recentlyprovided planned routes and which it expects will have logged speed datafor road segments on those routes.

In another alternative, the in-vehicle systems place the calls to theserver system to transfer logged speed data, but the server system haspreviously provided instructions to the in-vehicle system regarding whento initiate that call. For instance, when the server system provides aplanned route to the in-vehicle system, the planned route is accompaniedby an instruction to call the server system after the vehicle has passeda particular road segment.

In another alternative, whenever an in-vehicle system calls the serversystem, the server system optionally requests the vehicle's logged speeddata. In the case that the vehicle is calling for a route planningservice, the data transfer occurs during the interval between the uploadof the desired destination and the start of the download of the plannedroute, or in any other interval that would have otherwise been unusedfor data transfer from the vehicle to the server system.

In another alternative, when the server system provides a planned routeto an in-vehicle system, the planned route includes the server system'sup-to-date expected link times (i.e., the link times reflect recentlyreceived probe data). In this alternative, traffic exceptions on asegment are not reported to the server if the server system was alreadyaware of the exception at the time that it planned the route.

3.7 Data Fusion

In alternative versions of the system, the server system receivestraffic related information from external information services. Forinstance, the server system receives traffic incident reports (e.g.,breakdown reports) that it uses to predict slow travel speeds, ratherthan waiting to receive data from probe vehicles for those segments.Similarly, the server system receives information related to events(e.g., sporting events) that it uses to predict link speeds. The serversystem combines these predicted link speeds with link speeds reported byprobe vehicles when calculating new routes for in-vehicle systemsaccording to as shortest expected travel time criterion.

4 Vehicle Updating (FIGS. 20A-C)

In the system described above, in-vehicle system and the server systeminclude data that is kept consistent. For instance, the main roadsnetwork stored in the in-vehicle system includes a subset of the roadsnetwork on the server system. When the data is consistent, a destinationspecification that is validated by the in-vehicle system will be validfor the server system as well.

The information used by the overall navigation system is updated fromtime to time. For example, the map provider may provide periodic updatesto the road network to correct previous errors or to reflect changes inthe road network, such as addition of a new road.

Alternative versions of the system use one or more approaches toupdating the in-vehicle system to keep the in-vehicle and systemdatabases consistent. When the databases are consistent a destinationspecification that is validated by an in-vehicle system will not befound to be invalid by the server system when it tries to plan a routeto the destination. Conversely, when the databases are consistent, thein-vehicle will not rule out a destination specification that the serversystem would have found to be valid, for example because a new road hasbeen added to the road network.

The system also includes the provision to update the software inaddition to the data for the in-vehicle system. For instance, the userinterface for existing functionality can be changed by downloading newcode. Also, entirely new functionality can be downloaded. This new orchanged functionality can include modified menus and graphics that areused to interface with the operator.

New software and interface definitions are integrated into thein-vehicle system using one of several well-known alternativetechniques. For example, new software modules can provide predefinedentry points that are accessed from existing software modules in thein-vehicle system. Data describing the interfaces to new softwaremodules can be downloaded with the code that implements the modules.User interface definitions can be implemented using low-level code thatmanipulates the pixels on the display, or can use a high-leveldescription such as one using a markup language (e.g., HDML).

The navigation system uses one or more of the following alternativeapproaches to updating the in-vehicle system:

Physically replacing a static storage device in the in-vehicle system,

Updating over a high-speed data link, for example at a dealership orother service center, and

Updating over a cellular telephone based data link.

Each of these approaches are described in the following sections.

4.1 Physical Replacement of the Storage Device

Referring to FIG. 20A, in a first approach, static storage 222 inonboard computer 210 in in-vehicle system 105 is a removable device. Forinstance, static storage 222 can be a PCMCIA card housing a magneticdisk or a flash memory system.

Updating the in-vehicle system involves replacing storage device 222with another storage device 222 a that has been preloaded with anupdated version of the databases. This enables the entire database to beupdated quickly, for instance, when the main roads network needs to beupdated to correspond to a different geographic area.

4.2 Updating Over a High Speed Data Link

Referring to FIG. 22B, a second approach to updating the in-vehiclesystem involves transferring data to the in-vehicle system over ahigh-speed (e.g., up to 1 Mb/s) data connection. The in-vehicle systemincludes a data interface 2020 that is connected to onboard computer 210in in-vehicle system 105. A source of the update data is connected tothe data interface. For instance, a high-speed connection 2010 can beconnected to service equipment 2030 at a dealership or a service centerwhich downloads the updated information using industry standardcommunication protocols, such as Ford's SCP or the SAE J1850 protocol.Alternatively, an owner of a vehicle can connect a personal computer2031 (such as a laptop computer) to the in-vehicle system. Updates forthe in-vehicle system would be obtained by the owner on a recordedmedium 2040, such as a CD-ROM, or over the Internet. Connection 2011between the personal computer and the in-vehicle system can use awireless connection, such as an infrared link.

Referring to FIG. 20C, another alternative approach to updating thein-vehicle system is to use a wired telephone connection. In thisapproach, the in-vehicle system includes a moderate speed modem 2050(e.g., a 56 kb/s modem) and a telephone connector. The owner provides aphysical connection 2052 from the telephone connector to the publictelephone network (PSTN) 340. The in-vehicle system places a telephonecall to the server system, or another server used to provide dataupdates, and downloads the data at a moderate speed over the telephoneconnection.

4.3 Updating Over a Wireless Link

A third approach to updating the in-vehicle database uses a wirelessdata connections between the in-vehicle system and the server system,such as over a cellular telephone connection. The amount of data thatcan be transmitted in a reasonable time (e.g., less than an hour) islimited by the relatively slow data transfer speeds that can be achievedover such connections. Typically, the database is incrementally updatedover a wireless data connection rather than an entire new copy of thedatabase being downloaded.

One of several alternative approaches to initiating a database updateover a wireless data connection with the server system are used. First,an operator can explicitly request an update through the user interfaceof the in-vehicle system. Second, an update can be requested by anin-vehicle system based on an elapsed time since a prior update. Third,database edits can be downloaded prior to or after downloading a plannedroute after the in-vehicle system establishes a communication sessionwith the server system. Fourth, the server system can place telephonecalls to each of the vehicles and “push” the edit updates to eachvehicle in turn.

In order to maintain consistency between the in-vehicle data and theserver system's data, data in the database is associated with a versionnumber. Each time the server system updates its data, it updates theversion number. When a vehicle requests a route, it also provides theversion number of the data that was used to validate the destinationspecification of the route. The server system uses the received versionnumber to identify which, if any, updates have not yet been downloadedto the calling vehicle.

The server does not necessarily have to download all updates in onesession. Instead, it provides updates incrementally. In the incrementalapproach, the most relevant updates are provided first. For instance,the server system updates the main roads network in the city in whichthe vehicle typically travels prior to downloading updates for anothercity.

If an in-vehicle system has an out-of-date database, the validateddestination specification that it sends the server system may be invaliddue to changes in the road network. For instance, a street name may havechanged. Therefore, if the server system receives an invalid destinationspecification from the in-vehicle system, the server system notifies thein-vehicle system which notifies the operator. The operator can thenspecify another address, or wait for updated information to bedownloaded to the vehicle from the server system.

5 Additional Services

In addition to providing navigation services, alternative versions ofthe vehicle information system provide additional services such asroadside assistance, remote vehicle control, traffic information, andcommunication related services.

5.1 Emergency and Roadside Assistance

Emergency and roadside assistance provides an operator of a vehicle witha way of contacting assistance and providing the location of thevehicle. Referring to FIG. 21A, in an operator initiated interaction,the operator selects the emergency and roadside assistance option on theuser interface of the in-vehicle system. The vehicle places a cellulartelephone call to the server system, or to another server that thein-vehicle system has been configured to call to handle such requests.When the call is established, the in-vehicle system establishes a dataconnection to the called server. The in-vehicle system transfers aunique identification of the vehicle to the server. The uniqueidentification is used by the server to access information such as themake, model, and color of the vehicle, which may be useful to adispatched service vehicle finding the operator's vehicle. Thein-vehicle system also sends its estimated location, or raw GPS data,and most recent direction of travel based on its GPS measurements. Theserver system applies GPS correction data to the vehicle's estimatedlocation or raw GPS data to determine a corrected location estimate.After the in-vehicle system transfers the data to the server, theoperator can communicate with a telephone operator 2110 at the serverusing the telephone handset in the vehicle. This allows the operator toprovide details that may be useful in dispatching assistance.

In addition to operator-initiated requests for assistance, thein-vehicle system includes a mode in which activation of the air-bagsystem, or some other indication of an emergency situation,automatically initiates a request for assistance. This mode would beused, for example, if the vehicle is involved in a collision and theoperator is unable to or does not think to call for assistance.

5.2 Remote Vehicle Control

Another additional service is remote vehicle control. The in-vehiclesystem is coupled to vehicle subsystems, such as the door lockingsubsystem, or the vehicle control subsystem. This coupling can usestandard vehicle data communication infrastructure found in manyvehicles today, such as the SCP (the Standard Corporate Protocol) busfound in vehicles manufactured by the Ford Motor Company.

5.2.1 Door Unlocking

Referring to FIG. 21B, remote door unlocking is an example of a remotevehicle control service. When an operator is locked out of his or hercar, he or she contacts the server system, for example, by placing atelephone call to a telephone operator with access to the server system.After appropriate authentication by the telephone operator, thetelephone operator initiates a remote door unlocking procedure that isexecuted by the server system.

The vehicle's cellular telephone receiver is not typically left on whenthe operator has left the vehicle in order to reduce battery usage.Therefore, the server system does not, in general, simply make atelephone call to the in-vehicle system to unlock the doors.

On a precise schedule, the in-vehicle system repeatedly powers up thecellular telephone receiver to determine whether an incoming call isbeing placed at that time. For instance, the in-vehicle system repeatsthis cycle every 15 minutes. If the in-vehicle system does not detect acall, it powers down the telephone receiver until the next scheduledlistening time.

The vehicle's schedule is stored at the server system, and thein-vehicle system and the server system share a common time base, forexample based on GPS signals. The server system waits until the lockedvehicle's next scheduled listening time to make a cellular telephonecall to establish a data communication channel with the in-vehiclesystem. Once a data connection is established, the server system sends acommand to the in-vehicle system to unlock the doors.

When the operator of the vehicle requests the door unlocking servicefrom the telephone operator, the telephone operator informs the vehicleoperator of the time that the doors will be unlocked, since the scheduleof vehicle listening times is available to the telephone operator.

5.2.2 Vehicle Immobilization

A vehicle immobilization service uses a similar strategy as the doorunlocking service. A vehicle operator calls a telephone operator at thecentralized server to notify the telephone operator that the vehicle hasbeen stolen. The server system can either make a telephone call to thein-vehicle system immediately, if the telephone receiver in the vehicleis powered on, or relies on the scheduled power-up mode that is used forthe door unlocking functionality described above.

In either case, when the in-vehicle system and the server systemcommunicate, the in-vehicle system provides the vehicle's location tothe server system, and the server system provides to the in-vehiclesystem a command to disable the vehicle. The in-vehicle system thensends a command to a vehicle system to disable the vehicle.

5.3 Traffic Information

The traffic information service provides an operator with a report oftraffic conditions on a small set of previously specified “trips.” Forinstance, an operator may have a choice of three alternative ways ofgetting go from home to work. When the operator is about to begin thetrip, he or she interacts with the in-vehicle system to request trafficinformation on those trips. The in-vehicle system contacts the serversystem, which provides current traffic information for the operator'strips.

One approach by which the operator specifies his or her “trips” uses anonboard stored table of a set of trip segments. These segments wouldtypically involve many segments of the road network. For instance, aportion of a major highway between two intersecting highways might betrip segment. The operator “builds” the personal trips by choosing asubset of trip segments. When the in-vehicle system contacts the serversystem to determine traffic conditions on the operator's personal trips,the in-vehicle system transfers the operator's selected trip segments tothe server system.

The server system uses its traffic database, which include current linkspeeds on segments of the road network, to determine the current trafficconditions on the operator's trips. Various alternative presentations ofthe traffic conditions can be used. In this version of the system, thetraffic conditions are categorized into a small number of categories,such as normal, congested, and severely congested, and each category isdisplayed graphically to the operator using a different icon.

In alternative versions of the system, the server system activelycontacts a user if an exceptional traffic condition occurs on one of theuser's previously specified trips. For instance, the server system cansend the information to the in-vehicle system by calling the in-vehiclesystem, or send a pager message, send email, or place a telephone callto the user informing the user of the exceptional condition.

In another alternative, the user specifies several alternative trips.When the server system detects an exceptional traffic condition on oneof the user's specified trips, it actively downloads traffic informationrelated to the alternative trips. In this way, the user does not have towait for the in-vehicle system to make a call to the server system toreplan the route.

6 Extensible Server Architecture (FIG. 22)

Referring to FIG. 22, an alternative server system 125 a provides thefunctionality of the server system 125 described above, and in additionprovides an extensible architecture for providing other services to thevehicles. Server system 125 a includes multiple server computers coupledover a LAN 2205. Alternatively, the functionality of these servercomputers can be implemented on a smaller number of computers, or on asingle computer that implements all their functions.

Server system 125 a includes a gateway system 2210 that is coupled totelephone interface 320. Gateway system 2210 is used to provide acommunication gateway between vehicles 100 and server computers inserver system 125 a, and implements a message routing function so thatcommunication received from an in-vehicle system is directed to theappropriate server computer. Gateway system 2210 does not necessarilyhave to interpret the content of data passing between the server systemsand the vehicles.

The server computers include a navigation system 2250 on which thenavigation application described above executes. When an in-vehiclesystem initiates a communication session with server system 125 a torequest a route planning service, gateway system 2210 determines thatthe session should be connected to navigation system 2250 usinginformation provided by the in-vehicle system in the communicationsession. For instance, the in-vehicle system identifies the navigationservice in the initial portion of the data stream. Alternatively,different services implemented by server system 125 a have differenttelephone numbers that are assigned to telephone interface 320, andgateway system 2210 routes the communication to the appropriate servercomputer based on the number called by the in-vehicle system.

Navigation system 2250 implements the functionality of server system 125as shown in FIG. 5. That is, it includes an interface to GPS receiver325, and includes server map database 520, yellow pages database 522,and traffic database 524. Navigation system 2250 is coupled to mapprovider 2252, and a traffic information system 2254.

Another service provided by server system 125 a is implemented by acommunication system 2260. Communication system 2260 is coupled toexternal communication systems, including an email system 2262 and apaging system 2264. These external communication systems forwardmessages addressed to particular vehicles to communication system 2260.Communication system 2260 requests from gateway system 2210 that a datacommunication channel be established with the particular vehicles, andthen passes data and commands to the in-vehicle systems.

The in-vehicle systems in the vehicles include software modules thatcorrespond to the services provided by the server system. For instance,communication sent from communication system 2260 to an in-vehiclesystem is received by a communication module that interprets the dataand commands it receives. For instance, a message communication moduledisplays paging or email messages on the display of the in-vehiclesystem, or alternatively plays them as synthesized speech messages.

A news system 2270 provides a service which sends data to vehicles whichcorresponds to news stories that are of interest to a particular vehicleoperators. The news stories are provided by an external news service2272.

Server system 125 a also includes a remote configuration system 2230that is coupled to LAN 2205, and that is also coupled to the Internet.Using the remote configuration system, users of the navigation systemcan modify their records in user profiles 2232 that are stored at theserver system. A user's profile is downloaded by the server system tothe in-vehicle system in that user's vehicle, or can alternatively bestored on the server system. Information in the user profiles caninclude various types of information, including stored destinations thatthe user can select from when specifying a destination to the in-vehiclesystem. For instance, a user can specify a list of frequent destinationsover the Internet, and then later in the vehicle choose a particulardestination in that list by selecting from a display of the list by thein-vehicle system.

Another aspect of the user's profile relates to the traffic informationservice. Rather than having to define a set of trips using thein-vehicle interface, the user selects trips using a graphical map-basedinterface. For instance, an entire map of the highway system or the mainroads network is displayed. The user selects paths on the graph byselecting sequences of trip segments. These trips are downloaded to theuser's vehicle, or can be stored by the server system. If they arestored at the server system, when the user initiates a trafficinformation request in the vehicle, the in-vehicle system does notnecessarily transfer the specifications of the operator's trips, ratherit specifies the identity of the operator and the server system looks upthe operator's stored trips.

A user's profile can also include preferences such as particular roadsthe user wants to avoid. The user's profile can alternatively include atime saving above which the user is willing to use a road that he or sheotherwise wants to avoid.

A user also uses remote configuration system 2230 to input routeplanning requests. For instance, the user provides a destinationspecification to the remote configuration system and the server systemdownloads a planned route to the destination prior to the user enteringthe vehicle. The user can access the remote configuration system in avariety of ways, including over the Internet, and over a voice telephoneconnection interacting with an automatic speech recognition device atthe server. In addition to specifying a destination, the user can alsorequest notification of when he or she needs to start the trip in orderto get to the destination at a particular time. The notification can beby telephone, pager, or using any of a variety of other notificationmethods.

A new service is added to server system 125 a by adding a servercomputer, updating gateway system 2210 so that communication for thatservice is routed to the new server computer, and updating thein-vehicle system by adding a corresponding software module to each ofthe in-vehicle systems. The in-vehicle systems are updated either over acellular telephone connection, or over a physical connection, asdescribed above (see Section 4).

Alternative version of the system do not necessarily include all thefeatures described above. For instance, a traffic information system caninclude operator specified trips. The in-vehicle system contacts aserver system for traffic information for those trips. The in-vehiclesystem does not need a GPS receiver, or a map database, of otherfeatures to support this feature alone.

In another alternative, the in-vehicle system does not necessarilysupport autonomous route replanning. The in-vehicle system can contactthe server to replan the route, or to provide a map which it uses toreplan the route, when the in-vehicle system detects that the vehiclehas gone off-route.

An alternative version of the system provides a “detour” capability. Inparticular, an operator indicates a road segment that should be removedfrom a planned route, and the in-vehicle system plans a detour aroundthat road segment using its main roads database.

In another alternative version of the system, the server system plansand downloads several routes, for instance planned according todifferent criteria, such as shortest time, shortest distance, etc. Thein-vehicle system displays characteristics of the alternatives (e.g.,time, distance) and the operator selects one. If the server have not yetdownloaded al the routes, only the selected route is continued to bedownloaded.

In another alternative version of the system, additional data isdownloaded from the server system along with the route. For instancetraffic information is downloaded and displayed to the operator. Also,advertising information, for example, for restaurants along the routeare downloaded and displayed to the operator and the vehicle passesalong the route.

In another alternative, traffic information is downloaded to thevehicle, for instance, according to a set of trips that have beenspecified by the operator. The traffic information is displayed alongwith a map of the road network. Traffic information is indicated usingone of a variety of techniques, including text annotations, icons, orusing color.

In another alternative, the server system does not download spot maps tothe in-vehicle system. The in-vehicle system provides turn-by-turninstructions from the starting locations. For instance, the firstinstruction may be “proceed to street X,” accompanied by an arrowindicating the direction the street X.

In another alternative, the in-vehicle system has a main roads networkfor autonomous replanning, but does not include address-range data forvalidating street addresses. The in-vehicle system instead relies on theserver system to validate the street number specified by an operator. Inthis way, the in-vehicle system validates and address partially andrelies on the server system completing the validation.

The same server system can concurrently support in-vehicle systems withdifferent capabilities, such as the alternative capabilities describedabove.

Another alternative version enables an operator to specify a sequence ofdestinations. For example, the first destination can be a gas station,and the second destination is the operator's work. All the destinationsin the sequence are validated before the in-vehicle system contacts theserver system. The server system plans a route from the startinglocation to the first destination, and then from one destination to thenext. The server system downloads the entire planned route to thein-vehicle system.

It is to be understood that the foregoing description is intended toillustrate and not to limit the scope of the invention, which is definedby the scope of the appended claims. Other embodiments are within thescope of the following claims.

What is claimed is:
 1. A method for vehicle guidance comprising:providing a stored map of a road network in a non-volatile storage in avehicle; receiving at the vehicle from a server a planned route to adestination location; storing the planned route at the vehicle;providing instructions to an operator of the vehicle according to thestored planned route; tracking a location of the vehicle, includingdetecting whether the vehicle has deviated from the planned route; andif the vehicle is detected to have deviated from the planned route,planning a new route to the destination location using the stored map.2. The method of claim 1 wherein providing the stored map includesproviding a removable storage medium storing said map.
 3. The method ofclaim 2 wherein providing a removable storage includes providing acomputer disk storing said map.
 4. The method of claim 2 whereinreceiving the planned route includes receiving said planned route over awireless communication link.
 5. The method of claim 4 wherein providingthe planned route over the wireless communication link includesproviding said planned route over a cellular telephone system.
 6. Themethod of claim 1 wherein the planned route identifies a series of roadsegments in a road network.
 7. The method of claim 6 wherein the storedmap identifies a network of interconnected road segments in the roadnetwork.
 8. The method of claim 7 wherein the planned route identifiesat least some road segments that are not identified in the stored map.9. The method of claim 7 wherein planning the new route to thedestination includes planning a route along road segments identified bythe map between a location of the vehicle and a road segment identifiedby the planned route.
 10. The method of claim 9 wherein planning theroute between the location of the vehicle and a road segment identifiedby the planned route includes executing a shortest path search to findsaid path.
 11. The method of claim 9 wherein planning the route betweenthe location of the vehicle and a road segment identified by the plannedroute includes planning said route to join the planned route in thevicinity of the vehicle's deviation from the planned route.
 12. Themethod of claim 1 wherein the planned route identifies a road segmentthat is not represented in the stored map.
 13. The method of claim 1wherein the server plans the planned route using information notavailable to the vehicle.
 14. The method of claim 7 wherein the storedmap is a partial map that includes a first subset of roads of the roadnetwork but does not include a second subset of roads of the roadnetwork, the first subset of roads containing more major roads than thesecond subset, the second subset of roads containing more residentialroads than the first subset.
 15. Software recorded on a computerreadable medium for causing an in-vehicle computer to perform thefunctions comprising: receiving at a vehicle a planned route to adestination location from a server; storing the planned route; providinginstructions to an operator of the vehicle according to the storedplanned route; tracking a location of the vehicle; detecting whether thevehicle has deviated from the planned route; and if the vehicle isdetected to have deviated from the planned route, planning a new routeto the destination location using a map of a road network stored in astorage of the vehicle.
 16. A vehicle navigation system comprising: aserver, including a route planner; a plurality of in-vehicle systems,each including storage for an in-vehicle map database, and storage for aplanned route; a wireless communication system for passing data betweenthe server and each of the in-vehicle systems; wherein each of thein-vehicle systems includes a guidance system for accepting adestination specification, validating the destination specificationusing the in-vehicle map database, sending the validated destinationspecification to the server over the wireless communication system,receiving a planned route to the destination over the wirelesscommunication system, and guiding the operator to the destination; andwherein each of the in-vehicle systems further includes an autonomousroute replanning system for detecting whether the vehicle has deviatedfrom the planned route, and if the vehicle is detected to have deviatedfrom the planned route, planning a new route to the destination usingthe in-vehicle map database.